FreeFileSync Open Source File Synchronization

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FreeFileSync User Manual:

Volume Shadow Copy (Windows only)

FreeFileSync supports copying locked or shared files by creating a Volume Shadow Copy of the source drive. This feature can be configured via Menu → Tools → Options: Copy locked files.

Note
  • The volume snapshot created by the Volume Shadow Copy Service is only used for copying files that are actually locked.
  • Accessing the Volume Shadow Copy Service requires FreeFileSync to be started with administrator rights.

Troubleshooting

If you experience problems using the Volume Shadow Copy Service, a renewal of registration might help. Create and execute a cmd batch file and insert the following lines or enter directly via command line:
cd /d %windir%\system32
Net stop vss
Net stop swprv
regsvr32 ole32.dll
regsvr32 oleaut32.dll
regsvr32 vss_ps.dll
Vssvc /register
regsvr32 /i swprv.dll
regsvr32 /i eventcls.dll
regsvr32 es.dll
regsvr32 stdprov.dll
regsvr32 vssui.dll
regsvr32 msxml.dll
regsvr32 msxml3.dll
regsvr32 msxml4.dll
 
Reference: http://support.microsoft.com/kb/940032