Riddle of the Disappearing Drve Map

I’ve recently been called in to reorganize a small LAN consisting of an NT 4.0 Server with 7 attached workstations also running NT 4.0. Latest service pack is 6a. Security is not a big issue here and I’m just trying to get a handle on the layout.
I thought I knew all the basics, but this one has me stumped. When I map a shared drive on the server from a workstation, all is fine for that session. Trouble is, the map won’t reconnect on the next login. There are other drives that remap just fine, but they were set up before I stumbled onto the scene. I’ve checked all the obvious things. Any ideas?