OK, I once had an issue where multiple users were connecting to an Access database on a shared resource. As I recall, if the user opened up Access and then navigated to the file, all was well, but if they opened the MDB file from an Icon on the desktop it defaulted to granting them exclusive access to the database, which they could not get if somebody else was already connected. The result was the error you are getting.
Bear in mind that this was on Access 7.0, and applied to an MDB database, not and ADP project, but the solution was to include a parameter in the commandline for the icon that ensured the database was not opened exclusively.
If it's not practically useful, then it's practically useless.