The .ldb file plays an important role in the multiuser scheme of the Microsoft Jet database engine version 4.0. The .ldb file is used to determine which records are locked in a shared database and by whom.
Do the users have the proper rights to the shared folder to create and delete files?
Whenever the last user closes a shared database, the .ldb file is deleted. The only exceptions are when a user does not have delete rights or when the database is marked as corrupted; then, the .ldb file is not deleted because it contains information about who was using the database at the time the database was marked as corrupted.
This could cause your issues.
If the database is not open the the .ldb file exists try deleting it then open the database.
If you plan to share a database, the .mdb file should be located in a folder where users have read, write, create, and delete privileges. Even if you want users to have different file privileges (for example, some read-only and some read-write), all users sharing a database must have read, write, and create permissions to the folder. You can, however, assign read-only permissions to the .mdb file for individual users while still allowing full permissions to the folder.
The only other thing that comes to mind is if someone is opening the database with exclusive access. This would prevent others from getting in.