Boy we just went over this in another thread; Access with a JET backend was never designed to be used over a WAN. You need another solution. Here's a link to the other thread where this was discussed:
http://www.experts-exchange.com/Microsoft/Development/MS_Access/Q_24176041.html
There is also a hotfix available for some network issues, but really, you should not be running Access/JET over a WAN. Can't stress that enough.
JimD.