Looks like Citrix has a workaround, but they are still looking for a fix.

<u>Symptoms</u>
Users connecting with ICA sessions receive a blue background and the Windows GINA does not display after installing Microsoft Rollup 1 for Windows 2000 SP4 on Metaframe XP and MPS 3.0 Servers. The console might be unresponsive and have high CPU utilization within the winlogon.exe process.

<u>Cause</u>
Issue occurs after applying the Microsoft Update Rollup 1 for Windows 2000 SP4 (KB article ID 891861) to Metaframe XP FR3 Service Pack 4 servers and MPS 3.0 servers.

Read the workaround in CTX107051.

[Via Thincomputing.net]