An FYI for those that may be running Exchange2000/2003 in a clustered environment with BES3.6/4.0.

I've done some research and there have been some issues with Exchange2000/2003 and memory fragmentation. There were some suggested fixes - these switches /3GB, /USERVA=3030 - that could be added to the boot.ini file as well as a registry change to the "SystemPages" value in the HKEY_LOCAL_MACHINE|SYSTEM\CurrentControlSet\Contro l\Session Manager\Memory Management registry key. These issues seem to result when the remaining virtual memory blocks are not of significant size for the process that made the request.
They affect the following platform - Windows2000 Std/Ent, Windows2003 Ent and Exchange2000/2003.

I have also checked our corporate Exchange environment (clustered) with BESX4.0 and it does exist. The above modifications has reolved the issues.