Inheritance security rules violated while overriding member - SecurityRuleSet.Level2

Question

I have a class that inherits from Exception. In .NET 4, I started receiving a runtime error:

Inheritance security rules violated while overriding m

Answer 1

Had this problem when I was calling an assembly that had AllowPartiallyTrustedCallers attribute:

[assembly: System.Security.AllowPartiallyTrustedCallers]

Removing it solved my problem without switching to SecurityRuleSet.Level1.