mapped drives

I have a customer with 2k server and 2kpro stations. They are constantly telling me they get red x on thier mapped drives and normally they click on it and get in with the x being remove but now sometimes the x stays even while allowing access particularly on Private drives. I ran net config server/ autodisconnect:-1 at the server but it does not seem to help. Do you have any suggestions? I would rather not pay $245 to microsoft for this.
Thank You
Neal Pressley