Winlogon.exe crashes on 2008 r2 dedicated farm redirector

I am having an issue with our test RDS farm.   The farm setup is as follows:

1. 1 Dedicated Redirector
2. 11 Session Host servers
3. average 30 sessions/server

Each TS server 8CPU's /24GB ram

All 2008R2 RDS servers.

The Windows logon process has unexpectedly terminated.

Problem is with winlogon.exe terminating unexpectedly.  Memory climbs on theRedirector and eventually crashes.

I can't seem to find anything that helps, and I need some pointers as to what to look for as to why Winlogon.exe is crashing.

Thank,

Rob