I spent hours troubleshooting this the other day and want to make sure the community doesn't do the same! For current Altiris environments, this will become an issue as you upgrade your virtual environments!
Symantec Installation Manager (SIM) crashes with a Fatal Execution Engine Error.
Event Type: Error
Event Source: .NET Runtime
Event Category: None
Description:.NET Runtime version 2.0.50727.3615 - Fatal Execution Engine Error (7A0979AE) (80131506)
Client Management Suite 7.0 on Windows Server 2003 R2 and SQL Server 2008 on box – all hosted on ESXi 4.1
Symantec Installation Management 7.0.816
Known Issue in VMware ESXi 4.1 with Software Virtualization.
Essentially, if you are using Windows Server 2003 32-bit with the /3GB switch set in the boot.ini and your host is ESX 4.1 (or ESXi) then you will run into this issue.
The resolution steps in the below VMware KB article provide the instructions for enabling hardware virtualization (needs to be supported by the CPU) instead of Software Virtualization.