MS-Access - Multiple user problem with Vista (norton internet sec.

We moved from a network of 4 XP machines to a network of 4 Vista machines.
Now only one user at a time can get into access, unless the second user is
the one at the main Network PC.
I have went to the properties on the folder and MS-Access DB file on the
Network PC and then to the permissons and set all access to every and every
selection.
Still only one person can get in to the DB. This is causing a problem can
anyone give me some suggestions. I will be glad to e-mail screen prints of
settings.
Thank you Russ