MMC has detected an Error in a snap-in. It is recommended that you shut down and restart MMC.
In an Active Directory forest that is running a Windows Server 2008 schema, the Active Directory Users and Computers MMC snap-in may crash when you open the Properties dialog box for a user object from a Windows Server 2003 member server
http://support.microsoft.com/kb/946459/en-us
Error message when you open a Microsoft Management Console (MMC) snap-in after you install Windows Server 2003 Service Pack 2 or Windows Small Business Server 2003 R2 Technologies: "MMC has detected an error in a snap-in"
http://support.microsoft.com/kb/947532/en-us
MMC 3.0 update is available for Windows Server 2003 and for Windows XP
http://support.microsoft.com/kb/907265/en-us
