Upgrading from C5.5.3 to C6.5

Hi,
I recently bought the Cubase 6.5 update to update Cubase 5.5.3. I have installed 6.5 and updated the eLicencer. However 6.5 refuses to open. Do I have to have C 6 installed before installing the 6.5 update?

Regards.
David

No