We can't tell you "do this and it'll fix it" because we have no access to your code or data - and the chances are you will need both in order to get it working.
Best guess from this distance? The file format or type is newer than the Access engine you are using to open it.
Start with yoru connection string, which will specify the engine type (ACS or JET) and version that you are using.
Check here and see if you can work out what teh file version is, and if it's compatible: ms access - How can I tell the version of an ACCDB file? - Stack Overflow
Good luck - we really can't do much more for you!