Win XP Pro and disabled user fast switching

In anticipation of hijackers, spyware, and such, I recently installed several tools including Hijack This, Spybot, and spywareblaster onto my Win XP Pro machine.

Subsequently fast switching among users is no longer supported by the OS and it indicates that one of the programs disabled it. I'm curious if this is a well-known side effect of one or any of the above programs?

I believe the solution is to adjust the registry to force use of the default Graphical Identification and Authentication file (Msgina.dll).

Any comments/experience on this would be appreciated, including the proposed solution. Also, is there a fundamental reason one the programs disables that mode of XP?

thanks,

pas