Running .NET applications across the network

Hello all.
I am fairly new to vb.net and have written a couple of applications now but we are having real problems trying to run the apps over the network. It works on some peoples machines but not on others. When it does not work we get the standard "The operation required the SecurityException" message box.

Any help on this would be appreciated. Sorry this post is a bit vague.

Hmmm... three questions asked and five threads created. Please don't create duplicate threads.