A family of Microsoft relational database management systems designed for ease of use.
It's a bit hard to fix a problem that we can't see, but... two questions:
Are both databases in a Trusted Location?
Try opening the failing database; type Ctrl-G to open the VBA editor; and try compiling the application. Does it compile correctly, or give you an error? If it does, what's the error?
John W. Vinson/MVP