MSAccess: Currently locked by another user, could not update error

We are working with a 200mb MS Access 2003 database (zip attached) with about 50 users running MSAccess locally on their workstations and about 10 users logging in via Remote Desktop to the server. About once a day we are getting the error "Currently locked by another user, could not update" and we have to restart our server to clear the error, causing critical work stoppage. We are currently running Windows 2003 Enterprise SP2 with 16GB RAM. We would like some help to fix this error permanently - it's random and we can't seem to pin down what the cause might be. If necessary we can go to Windows 2008 R2 on the server and/or upgrade to Access 2010 if that might help. You can take a look at the attached zip file in case you see in clue to help fix.