Thanks for your rapid response.
I am not integrating into a Photopost database (as far as I know). I have opted to integrate with an existing vBulletin database for users, but for Reviewpost to also have its own database for whatever it needs to store.
The two database names and separate users have been entered correctly in the config file.
The only question I am seeing in step 4 relating to prefixes is in respect of my "Forums database table prefix". I have no idea whether there is one. If that is the issue, how could I find out, please?