MS Access Multi-user not working

I recently moved a MS-Access DB from a Xp operating system with 4 PC-s networked running Norton Internet Security 2006 to
a new set of PC-s running Vista Business. I am not have a serious issue of only one user being allowed in the database at a time. I have update the permissions on the PC the DB resides on the folder and file to for all users to allow everything. One more item if you are accessing the DB from the PC where the DB resides you can get in if another PC is in. Otherwise you cannot. I heard of other people having multi-user MS-Access DB problem.
Any ideas to fix the issue will be appreciated.
Thank you
Russ