Over a period of two months, our IIS hosting Kaseya crashed every few days.

The error message was: "A process serving application pool 'ASP.NET v4.0' suffered a fatal communication error with the Windows Process Activation Service. The process id was '3136'"

It seems that after a long search, the cause is found. 

We implemented this fix: http://support.microsoft.com/kb/831135 and the issue was gone.

Hoping this helps others.