MetaFrame XP, unlike MetaFrame 1.8, does not experience this problem.
A UPN greater than 20 characters supplied to Program Neighborhood is truncated by Termsrv.exe at logon to a MetaFrame 1.8 for Microsoft NT Server 4.0, Terminal Server or Windows 2000 Server. Termsrv.exe passes the truncated credentials to Winlogon.exe during the logon process. This issue can be reproduced with an RDP client connection supplied with autologon information.
Note: This issue should not occur on systems with SP1 or later.
Unlike MetaFrame 1.8, MetaFrame XP employs CtxGina.dll for its logon process. CtxGina.dll intercepts a call to GetAutologonCredentials to prevent Termserv.exe from truncating user names more than 21 characters.