If you are using the Volume Shadow Copy Service (VSS) software provider on a system running Windows 7 – Service Pack 1, Windows Server 2008 R2 – Service Pack 1 or Small Business Server 2011 – Service Pack 1 then you may find the computer randomly stops responding.
This occurs because volsnap.sys tries to obtain a lock again on a file even if it is already holding a lock.
A hotfix can be requested to resolve the issue using KB 2627052 http://support.microsoft.com/kb/2627052