Error installing PSP 7.50A on Citrix servers

[SIMUser]

Two of three Citrix servers upgraded to psp 7.50a are showing this behavior. Win2k3, Presentation server 4 on ProLiant DL360 G4s.

vcagent.exe errors with this message when trying to start it:
The exception unknown software exception (0x06d007e) occurred in the application at location 0x77e649d3.

I believe it's related to this in the event log, but do not know for sure:
Event Type: Information
Event Source: EvntAgnt
Event Category: None
Event ID: 2020
Date: 5/19/2006
Time: 2:23:12 PM
User: N/A
Computer: CTX---
Description:
SNMP Event Log Extension Agent has terminated.

The SMH is unavailable.

I've tried uninstalling, rebooting, and reinstalling all of the agents. Then tried uninstalling all of the agents and SNMP, rebooting, and reinstalling those. So far to no avail.

Any ideas?