After installing SharePoint Server 2007 on Windows Server 2008 R2, you may start to see the following error message in the event logs :
Volume Shadow Copy Service error: Unexpected error calling routine RegOpenKeyExW(-2147483646,SYSTEM\CurrentControlSet\Services\VSS\Diag,…). hr = 0×80070005, Access is denied.
Inspection of the detailed tab of the event log entry will show information about the process that generated the error. Take note of the user mentioned after the “- User: Name:” portion of the bytes. To resolve this error, simply give that user full permission to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\VSS registry key.