When you're developing .NET apps the .NET security can be a right pain in the butt, so to avoid any more head aches you can simply turn it off by using the caspol utility eg:
caspol -s off
While this is somewhat overkill (much like cutting your toe nails with a sythe), it certainly gets you up and running in no time. However the problems come when you start moving from your dev platform, onto testing & prod environments. But hopefully with you'll implement a more thorough approach.
This works fine for .NET 1.0/1.1, however for .NET 2.0 they have changed this so you can no longer ditch security in such a wide sweeping fashion. Here they still allow 'caspol -s off' however it is only effective while the cmd shell is open. Another method for .NET 2.0, is via the .NET Configuration tool - just update the security settings for the zone you use.
HTH
Tim