Error Msg on Shut down

I am running Win2K Pro w/all SP’s and Hotfix’s. When I restart my system, I get the following:

Application popup: explorer.exe – Application Error : The instruction at “0x00404d51” referenced memory at “0x00000000”. The memory could not be “read”.

MS TechNet has an entry regarding a Citrix or Terminal Server, but I am running neither. Also, my Spy Sweeper will not shut down automatically, I must manually “End Program”. WebRoot tech support has been no use. Could these two issues be conected? I have uninstalled and reinstalled Spy Sweeper a half dozen times. Any thoughts would be appreciated.

Doug