A "shared" drive could be either network-attached storage (NAS) or a drive on a Windows-based server.
Failure to delete the .LACCDB file for NAS could be related to permissions, but since the NAS usually doesn't have a formal O/S, it is hard to test whether someone actually still has the file open. All you can do for NAS is verify DELETE permission in the folder holding the file and, of course, DELETE permission for the file itself. (Obviously, if it is open, you already have READ permissions on folder and file.)
For the served-by-Windows case, however, it is possible to use the command prompt (CMD) to look at file locks via the OPENFILES command and determine the process ID of the process that is keeping it open. NOTE: To be able to disconnect the culprit connection, you must run CMD as Administrator. You can type OPENFILES /? to see what commands are available.
EDIT: You posted while I was researching... OK, for the Server-based case, you can look to see who has it open by connection name and can then disconnect it.