The whole game directory is normally listed when you press Ctrl-G, but one game should be highlighted, which is intended to be the game which gamebase will run. If it is the wrong game, or no game is highlighted it suggests that the Gamebase .mdb file has possibly become corrupt.
Have you checked the 'Filename' field in the Games table using MS Access or equivalent? It should contain the correct file reference. If an incorrect or corrupted name appears here, that will be your problem and it will be a ball-ache to fix each entry.
How about downloading a fresh copy of the database (for GB64 in your case I think), re-installing it and we'll take it from the top?
Also, when I did a restart Win XP, detected that the GBC_v02.ldb created a file error problem. Maybe this has something to do with it?
Well... there are some clues, but I'm not sure of the suffix;
i.e. As you will know, there is a C64 database currently referenced GBC_v02 , but Gamebase creates .mdb files, not .ldb's
It's fairly obvious there is a relationship, but I don't know what it is.
A quick search on the internet found that ldb is either a 'Lipid Database'
...or a debugger associated with ANSI C programs, which might be getting close but Gamebase is written in VB???
Anyway, unless you have been invaded by lipids, I reckon it's fairly safe to say you just have a corrupted database. Again, try the suggestion a couple of para's above.