Romcenter

Hello, I feel like I did something wrong and I am not sure what is causing me to get this error. Anyone know how to fix this?

Database extension not supported. Must be '.rdt'
Romcenter will now close.

Well, it seems pretty obvious. The database file you are trying to open must have .rdt as extension. You probably accidentally renamed it and deleted the extension. I'm guessing it's "name" instead of "name.rdt".