Hi Juggles!
How often have you installed Divine Divinity? Because i know from several cases with a corrupt installation although a correct installation has been notified.
But anyway, even a corrupt installation should not effect the patch, because he just search the registry where to find the right path...
Perhaps he get confused by too many partitions? Have an idea: just decrease the number of your partitions (i.e. only two) and then try again! No, was just a joke...