I have an issue with the SMS_SITE_BACKUP. getting 32 errors but those files are not using by any process. We have verified using the sysinternals tools (process monitor and process explorer)

Registered connection to SQL server xxxxxxxxx.com and database CASDB01\CM_CAS. SMS_SITE_BACKUP 7/26/2015 2:57:18 AM 16096 (0x3EE0)
Registered connection to master database on SQL server xxxxxxxxx.com. SMS_SITE_BACKUP 7/26/2015 2:57:18 AM 16096 (0x3EE0)
Initializing the status message reporting system... SMS_SITE_BACKUP 7/26/2015 2:57:18 AM 16096 (0x3EE0)
    The path to the "Status Manager" inbox is "G:\Program Files\Microsoft Configuration Manager\inboxes\statmgr.box\statmsgs". SMS_SITE_BACKUP 7/26/2015 2:57:18 AM 16096 (0x3EE0)
    SMS_STATUS_MANAGER is not running as part of this process, the SMS_EXECUTIVE to SMS_STATUS_MANAGER in-memory status message queue will not be used. SMS_SITE_BACKUP 7/26/2015 2:57:18 AM 16096 (0x3EE0)
Registered this process as a source of "SMS Server" events. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Registered this process as a source of "SMS Client" events. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Registered this process as a source of "SMS Provider" events. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Status message reporting system initialized successfully. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Locale set to OS value (English_United States.1252). SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
SMS_SITE_BACKUP service 2012 started. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
STATMSG: ID=500 SEV=I LEV=M SOURCE="SMS Server" COMP="SMS_SITE_BACKUP" SYS=xxxxxxxxx.com SITE=CAS PID=27980 TID=16096 GMTDATE=Sun Jul 26 00:57:20.150 2015 ISTR0="SMS_SITE_BACKUP" ISTR1="" ISTR2="" ISTR3="" ISTR4="" ISTR5="" ISTR6="" ISTR7="" ISTR8="" ISTR9="" NUMATTRS=0 SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Starting backup - Sun Jul 26 02:57:20 2015 SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
SMS installation root directory = G:\Program Files\Microsoft Configuration Manager. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Warning: SQL installation root directory is empty.The registry key "SOFTWARE\Microsoft\MSSQLServer\Setup\SQLPath" (populated by ConfigMgr setup) was found empty. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Site server backup location = G:\CMBackup. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
SQL backup location = G:\CMBackup. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Warning: Backup location and the sms root directory are on the same volume G. Sms Backup creates snapshot of the volume using VSS services and then copies the data to the backup location. It is advisable to have the backup location on a different volume than the one that has SMS data, so that the writes to the volume is minimal when the volume snapshot is active. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Verified that backup folder G:\CMBackup exists. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Verified backup service has permission to access the backup folder G:\CMBackup SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Sql Writer service is running. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
STATMSG: ID=5055 SEV=I LEV=M SOURCE="SMS Server" COMP="SMS_SITE_BACKUP" SYS=xxxxxxxxx.com SITE=CAS PID=27980 TID=16096 GMTDATE=Sun Jul 26 00:57:20.189 2015 ISTR0="" ISTR1="" ISTR2="" ISTR3="" ISTR4="" ISTR5="" ISTR6="" ISTR7="" ISTR8="" ISTR9="" NUMATTRS=0 SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
LogEvent(): Successfully logged Event to NT Event Log. (4 - 48 - 1,073,746,879) SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Starting VSS initialization... SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Starting Asynchronous GatherWriterMetadata. SMS_SITE_BACKUP 7/26/2015 2:57:20 AM 16096 (0x3EE0)
Number of writers that responded: 16. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Reading SMS Writer metadata... SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Number of FileIncludes: 0. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Number of FileExcludes: 0. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Number of Components: 7. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Component 0 - CASBackup\SiteServer\SMSServer\inboxes. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
FileGroupFile = G:\PROGRAM FILES\MICROSOFT CONFIGURATION MANAGER\INBOXES\* [Recursive: yes] SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Volume G:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Component 1 - CASBackup\SiteServer\SMSServer\Logs. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
FileGroupFile = G:\PROGRAM FILES\MICROSOFT CONFIGURATION MANAGER\LOGS\* [Recursive: yes] SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Volume G:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Component 2 - CASBackup\SiteServer\SMSServer\data. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
FileGroupFile = G:\PROGRAM FILES\MICROSOFT CONFIGURATION MANAGER\DATA\* [Recursive: yes] SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Volume G:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Component 3 - CASBackup\SiteServer\SMSServer\srvacct. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
FileGroupFile = G:\PROGRAM FILES\MICROSOFT CONFIGURATION MANAGER\SRVACCT\* [Recursive: yes] SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Volume G:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Component 4 - CASBackup\SiteServer\SMSServer. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
FileGroupFile = G:\Program Files\Microsoft Configuration Manager\install.map [Recursive: no] SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Volume G:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Component 5 - CASBackup\SiteServer\SMSbkSiteRegSMS.dat. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
FileGroupFile = G:\Program Files\Microsoft Configuration Manager\BackupTemp\SMSbkSiteRegSMS.dat [Recursive: no] SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Volume G:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Component 6 - CASBackup\SiteDBServer\SMSbkSQLSiteDB.dat. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
Dependency On SQL Writer , LogicalPath:CASSCCM2012\CASDB01, ComponentName:CM_CAS SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
SQL Server is on the same box as the Site Server. So, no need to communicate to the SQL backup agent. SMS_SITE_BACKUP 7/26/2015 2:57:21 AM 16096 (0x3EE0)
FileGroupFile = H:\Program Files\Microsoft SQL Server\MSSQL11.CASDB01\MSSQL\DataCM_CAS.mdf [Recursive: no] SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
Volume H:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
FileGroupFile = E:\Program Files\Microsoft SQL Server\MSSQL11.CASDB01\MSSQL\DataCM_CAS_log.ldf [Recursive: no] SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
Volume E:\ (that contains the file(s)) is marked as a candidate for snapshot. SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
After GatherWriterMetadata SQL Writer status = STABLE. SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
After GatherWriterMetadata SMS Writer status = STABLE. SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
Starting Prepare for backup. SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
The System Provider VSS ID is 0,000,000,000,A69,498 SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
Added volume containing G:\ to the snapshot set. SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
Added volume containing H:\ to the snapshot set. SMS_SITE_BACKUP 7/26/2015 2:57:22 AM 16096 (0x3EE0)
Added volume containing E:\ to the snapshot set. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Info: Starting Asynchronous PrepareForBackup... SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Info: Asynchronous PrepareForBackup finished... SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
After PrepareForBackup SQL Writer status = STABLE. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
After PrepareForBackup SMS Writer status = STABLE. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Starting to clean the backup location G:\CMBackup\CASBackup. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Deleting file G:\CMBackup\CASBackup\SiteDBServer\CM_CAS.mdf, FAILED, Win32 Error = 32 SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Failed to delete the contents of the backup folder. Error = [error code: 0, error message: The operation completed successfully.] SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Error: Deleting the existing files in the backup location failed. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Aborting the backup process. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
STATMSG: ID=5026 SEV=E LEV=M SOURCE="SMS Server" COMP="SMS_SITE_BACKUP" SYS=xxxxxxxxx.com SITE=CAS PID=27980 TID=16096 GMTDATE=Sun Jul 26 00:57:23.681 2015 ISTR0="G:\CMBackup\CASBackup" ISTR1="" ISTR2="" ISTR3="" ISTR4="" ISTR5="" ISTR6="" ISTR7="" ISTR8="" ISTR9="" NUMATTRS=0 SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
StateTable::CState::Handle - (5026:3 2015-07-26 00:57:23.681+00:00) >> (5057:1 2015-07-23 05:50:42.288+00:00) SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
CStateMsgReporter::DeliverMessages - Queued message: TT=1401 TIDT=0 TID='EF736CF9-7214-4796-9C85-2549A9056D8D' SID=5026 MUF=0 PCNT=2, P1='CAS' P2='2015-07-26 00:57:23.681+00:00' P3='' P4='' P5='' SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
CStateMsgReporter::DeliverMessages - Created state message file: G:\Program Files\Microsoft Configuration Manager\inboxes\auth\statesys.box\incoming\r5mx91tp.SMX SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Successfully send state change notification EF736CF9-7214-4796-9C85-2549A9056D8D SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
SMS_SITE_BACKUP failed. Please see previous errors. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
STATMSG: ID=5060 SEV=E LEV=M SOURCE="SMS Server" COMP="SMS_SITE_BACKUP" SYS=xxxxxxxxx.com SITE=CAS PID=27980 TID=16096 GMTDATE=Sun Jul 26 00:57:23.703 2015 ISTR0="Error: Deleting the existing files in the backup location failed." ISTR1="" ISTR2="" ISTR3="" ISTR4="" ISTR5="" ISTR6="" ISTR7="" ISTR8="" ISTR9="" NUMATTRS=0 SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
SMS_SITE_BACKUP service is stopping. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
STATMSG: ID=502 SEV=I LEV=M SOURCE="SMS Server" COMP="SMS_SITE_BACKUP" SYS=xxxxxxxxx.com SITE=CAS PID=27980 TID=16096 GMTDATE=Sun Jul 26 00:57:23.705 2015 ISTR0="SMS_SITE_BACKUP" ISTR1="" ISTR2="" ISTR3="" ISTR4="" ISTR5="" ISTR6="" ISTR7="" ISTR8="" ISTR9="" NUMATTRS=0 SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
Raised backup task failure alert. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
SMS_SITE_BACKUP service stopped. SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)
STATMSG: ID=501 SEV=I LEV=M SOURCE="SMS Server" COMP="SMS_SITE_BACKUP" SYS=xxxxxxxxx.com SITE=CAS PID=27980 TID=16096 GMTDATE=Sun Jul 26 00:57:23.727 2015 ISTR0="SMS_SITE_BACKUP" ISTR1="" ISTR2="" ISTR3="" ISTR4="" ISTR5="" ISTR6="" ISTR7="" ISTR8="" ISTR9="" NUMATTRS=0 SMS_SITE_BACKUP 7/26/2015 2:57:23 AM 16096 (0x3EE0)

Well normally this error Win32 Error = 32 SMS_SITE_BACKUP this mean the file was in use either by VSS or by something else.

The easy way would be to do a reboot and this should fix the issue. After the reboot go in the service and start the backup service if you can this will run the backup job right away and you can test this.

On a side note i strongly suggest dropping the SCCM backup job and replacing it with a Data base backup this is 100% supported for restore and a lot more efficient.