Windows Backup failed while trying to read from the shadow copy on one of the volumes being backed up. Please check in the event logs for any relevant errors.
Error code: 0x81000037
My system was a Windows 7 x64 Ultimate, and I was backing up to an internal HD, so nothing could be more standard
After some searching I’ve found that the problem was generated indirectly from windows media player: after configuring music library it added the root music location to system libraries. I manually removed the item from the sys libraries and … wow ! now works !
The problem (maybe) was that the link in the sys libraries was pointing to a folder that is a mount point for another internal HD with all my music stuffs.