Full backup not completing

I have been using TIH 10 for a long time now to take weekly full image backups of my Windows XP C-drive with no problems (I have recovered several times from the latest image). But when I ran it today it seems to reach just over a minute to completion and then hangs. This happens whether I run it under Windows XP or booting from the TIH CD. I have tried using different external drives to save the image onto and there is plenty free space. The log file shows the last entry to be 'Locking Partition C: ...' and nothing else. The last entry in the log file of the last successful image backup is 'Operation has succeeded'. Has anyone come across this before?