User Logon Screen

I am managing a small network of 300 machines, consiting of mostly WIN98 and some WIN95, WINNT4.0, and one or two WIN2000. Recently , some of my Dialup machines are having problems logging in. They dial an ISP then VPN into our network using Microsoft’s VPN adapter. Instead of getting the normal Microsoft Network Password Screen thet get a User Logon Screen (Not Windows Logon). This screen will not go away and will not let them logon to our network. I can not find any info on this from Microsofts TechNet. Has anyone seen this before?