Welcome! and rules
Joel on Software
.NET v1.1 changes delegate accessibility checking!
From the GotDotNet .NET 1.1 backwards-breaking change log: http://www.gotdotnet.com/team/changeinfo/Backwards1.0to1.1/default.aspx#00000139
Not sure why they did this, but it seems logical that delegates would undergo the same ACL-checking that all other CLR resources do. Just because you have a delegate reference doesn't necessarily mean you have any rights on it.
Well, it does mean you have rights on it... As Marcus mentioned, you couldn't have gotten the delegate in the first place unless it were provided to you directly or if you had retrieved it using a method or property that you did have access to. It's really no different than being provided a reference to a private field or property of an object -- if another object receiving the reference (say, as an argument to one of its methods) doesn't have proper access to the private member that the reference goes to, that still doesn't keep it from using the reference.
YOU have rights on it.
This change was also included in .NET v1.0 SP2.
The change you're talking about isn't quite what you think. Check out this thread from the DOTNET-CLR list over on discuss.develop.com:
Fog Creek Home