I have added a system to a Protection Group for System State and BMR, but the Protection Status shows "Replica is inconsistent".  When I check the job in Monitoring, I see "DPM failed to create the backup.  If you are backing up only System State, verify that if there is enough free space on the protected computer to store the System State backup"  I have 145GB\272GB free on the client computer. 

1. How much free space is necessary?

Hi,

For BMR backup, there is no minimum free space requirement on the protected server.  Be sure the Windows backup feature is installed and check to be sure the replica volume on the DPM server is large enough to hold the size of the protected system drive.

Please review the following blog: http://blogs.technet.com/b/dpm/archive/2011/10/31/troubleshooting-data-protection-manager-system-state-and-bare-metal-backup.aspx