This error is happening when only one user clicks the shortcut to the database. While trying to open the database he receives this error when someone else is in the database.
If no one is in the database he can open just fine without an error message.
It is happening with all databases stored on server if someone else has opened it first.
Checked file associations. Verified all settings are the same. I have reinstalled Office Professional and it worked correctly for about two weeks and then started to repeat the initial problem as stated above.
He can open the database while someone is in it if he launches Access first then uses File, Open but not from the shortcut or database on server.