This usually means there is some security issue - the most common is lack of adequate permission to access the server you are trying to access. Could you describe what you are doing - which os, which server, what are the security settings (if you know). You can also check Control Panel -> Administrative Tools -> .Net Framework Configuration. Go to the Configure Code Access Security Policy, Increase Assembly Trust. Select the network.dll. I've seen claims this should help: let us know if you could...