Quickmap may give this error:
Quickmap Initialisation Error
Could not open database
Additional Information: Could not start session. Too many
sessions already active.
To understand why this happens, we must first understand how Microsoft Access works. When you connect to an Access database (MDB), an LDB file is created in the directory containing the MDB file, and your name is inserted into the LDB file (which is basically a text file). Each subsequent user connecting to the MDB has their name appended to the LDB file. When users disconnect from Access, their name is removed from the LDB file, and the LDB file is deleted when there are no more users. Access has a restriction that only 256 names can be added to the LDB file. Once this threshold is reached, you get the message Too many sessions already active.
So understanding this, Quickmap may show the above error if users names cannot be removed from the LDB file (which may be a permissions issue, or just that Access has been unable to perform the function correctly – deleting the LDB file may fix the latter scenario), or if there are over 256 users sharing the same MDB file. Interestingly, if permissions are set such that users are unable to create an LDB file where one does not already exist, Access is also quite happy, which makes this an alternative option as a fix, rather than correcting existing problems.