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: 

• In Windows XP and Server 2003: Click 'Start' > 'All Programs' > 'Accessories' > 'Command Prompt'.
• In Vista/7/8 and Servers 2008/2011/2012 follow steps from a.
  (Note: if at START screen in Windows 8 start at b.) 
  
  1. Press keyboard ?Windows key?
  2. Type word 'command'
  3. Then right-click on ?Command Prompt?
  4. From menu click 'Run as administrator' (in Windows 8, menu is at bottom of screen)

Enter 'Y' if you receive the 'schedule this volume..' message.