It seems that after my recent post moaning about Windows Backup it has decided to get it's own back and now refuses to run with an unhelpful, incorrect (and ungrammatical) error message! When tried to run my Backup (complete system image and selected User Data folders) it failed. The additional information pop-up box stated the following (in semi-English): "Windows Backup skipped backing up system image because one of the critical volumes is not having enough free space. Free up some space by deleting unnecessary files and try again. Error code: 0x81000033" Note that the Windows Backup pane has the following information clearly displayed at the same time: "Location: Backup_1 (G:) 71.52 GB free of 232.88 GB Backup size 10.98 GB" So Windows Backup thinks it has 71GB space free ... and it tells me there isn't enough space. That's helpful. It doesn't even tell me which "critical volume" needs more space (in fact now I know that space is not the problem). A search for the error code reveals no information. The event log has no further information. It fails after it creates the folder <ComputerName> (ie. the UserData part of the backup) on drive G: This contains about 10.5GB of new data so it has (nearly?) completed the backup of User Data. So this isn't a problem of the drive being inaccessible or unwritable. From previous backup I know the User Data part (<ComputerName>) will be about 11GB. And the System part ("WindowsImageBackup") will be about 20GB. So why does seem to think it doesn't have enough space when there is 71.5GB free on the Backup Volume? All volumes on the PC have spare capacity, even those which are not being backed-up, or are not involved in the backup. C: - 11GB free (and 18.5 GB used) - C:/D:/E: are partitions of the main hard drive (RAID) D: - 33GB free (temporarily empty) E: - 318GB free (about 11GB of data in folders selected for backup, other archives managed seperately) (F: is optical media) G: - 85GB free initially (150GB used) - backup destination - this is a physcally different hard drive H: - 10GB free (not relevant to the Backup used for online archival) - this is another physcally different hard drive Backup is set up to write data from C: and E: to G: I have checked drive G: for errors and chkdsk reports that it is all OK. There are no other error messages. The system Event Log has identical text to the message I get from Windows Backup, so it provides no useful information. So what is Backup trying to do? And why doesn't it produce any useful information? ............. Additional Information Updated 7/7/11 ................. The Volume Shadow Copy service is complaining that there is not enough space, somewhere, on some drive, without providing any more information. So I made certain that there is sufficient space on each possible volume (also those volumes which are not involved). a) I resized C: so that it had 60% free space in case Shadow Copy Service is trying to fill the C: drive with a copy of all the system. b) I resized the System Reserved volume to 50% free space in case Shadow Copy is messing with this. c) I cleared 15GB space on drive H: (not relevant) in case Backup has a problem with nearly full drives. d) I used vssadmin to check Volume Shadow locations and re-set the limit for the Shadow Storage on C: to "unlimited" in case this was a problem. None of these made any difference. I conclude that the Shadow Copy Service is having a problem either accessing or writing to something, somewhere. The "not enough free space" message seems to be incorrect. I guess it should be a permisson / access error message. I cannot find any way to get further information about this. I hope there is some way to debug Shadow Copy by (options in service properties?) but can find no help. How do I debug this? Some questions for the people who developed Windows Backup to consider: 1) Why is Backup (or Shadow Copy) not capable of indicating where the problem lies? 2) Why is there no further information in the System Event logs. 3) Why is Backup not capable of directing the temporary Shadow Copies to another drive. (Or to the memory - there is a system managed Pagefile on drive E: which could expanded to 300GB.) 4) I have found documentation explaining how to re-direct the volume shadow copies to another drive - in Windows 2008 Server. How do I do the same with Windows 7?