Resolution:
If BWC 5.3 Beta was installed on the system it leaves some leftover registry keys and this might result in 'Invalid Document Repository Path' when installing BWC 5.3 GA. This was a defect in Beta and fixed in BWC 5.3 GA.

The fix is simply to use regedit and delete the key prior to installing, or if you have already installed to update the path in the key to match your current GA installation.

Check for the following keys:
HKEY_LOCAL_MACHINE\SOFTWARE\TIBCO Software Inc.\TIB/InConcert Repository Server HKEY_LOCAL_MACHINE\SOFTWARE\TIBCO Software Inc.\TIB/InConcert Repository Server\7.2.0
HKEY_LOCAL_MACHINE\SYSTEM\CureentControlSet\Services\TIBInConcert Repository Server