This article explains a possible solution for the following error displayed in an image backup log:
Backup aborted! - Unable to read from disk - Error Code 121 - The semaphore timeout period has expired
The problem is likely to be caused by a file system problem on the source drive that is being imaged.
Run 'chkdsk c: /r' from a command prompt.
Note: Replace 'c:' with the drive letter that you are imaging.
Note: The '/r' switch is important and will cause the entire file system to be checked for bad sectors. This will require a reboot to complete and may take some time.
To open a command prompt:
Enter 'Y' if you receive the 'schedule this volume..' message.