This & other issues I have posted recently were all related to the same thing
- the use of conditional formatting in subforms (Access 2002, the mdb file is
in 2000 format).  

MSACCESS.exe was found to be running under the Processes tab in Task Manager
on the affected workstations.  Sometimes there would be multiple instances of
MSACCESS.exe because of this.  This was my first clue & I was able to isolate
the application (one of two with sub forms).  Armed with this knowledge, I
searched this forum and found the answer.  I removed the conditional
formatting & the problems went away!

Symptoms we had were:

1)  Users unable to open mdb file by double-clicking after opening & closing
the offending application (workstation thought Access was already running).
2)  Only way to open .mdb file was by opening Access on the workstation, then
opening the mdb file.
3)  .ldb file persisted even after all users closed out of the Application
(because the process was still running)
4)  Other Access Applications started "misbehaving" (would not open once
offending App was closed)
5)  Screaming, multiple phone calls,  and hair-pulling

As a side note:  it was this forum that solved the riddle.  I am fairly new
to Access & have found this forum to be a great resource.  (I am more
familiar with Oracle Forms & Reports).  

Thanks!