ANSWER:
This error usually means that the folder that contains the project .MDB file does not have full access for the person that gets this error. Changing security settings to give that person (or a user group to which the person belongs) full access usually solves the problem. If not check the security setting on the .MDB file itself and make sure that the person or user group has full access.
If you are still getting the error, look for an old .LDB file and delete it.