Mapped drives disconnected after login

I was asked to look at one network recently, and came across a strange problem. Upon login, the login script maps network drives (H, S, X). However on all workstations (windows 98, ans there arent many) it seems that as soon as they are connected windows 98 disconnects them. I think this might be related to the fact that they used to map drives with a “Reconnect on logon” checkmark, but I deleted the registry entry for that, and although new drives are no longer connected, existing ones are still disconnected. Can anyone shed some light on this?
Thanks