Hmm "Operation could destabilize the runtime" sounds too scary, what operation on earth is this; which can destabilize the .Net runtime?

It looks like  the 1.1 C#/VB.Net compiler had case boundary with the generated IL code, the massive overhaul done for the new features in 2.0 forced some low level code changes in CLR; this in turn is haunting few 1.1 assemblies.

One of the well known case is the switch statement having more than 8 conditions. If you try to use 1.1 assembly having a code block of switch statement exceeding 8 conditions then you might face the horrifying exceptions like...

System.Exceptions.PageLoadException

System.Security.VerificationException

Try changing the switch case to if..else condition that will solve the problem.

For more details check the below given link

http://forums.asp.net/thread/1255521.aspx