Okay, so I've been trying to create a UDP Server (I've got the TCP one done but I need both for my project). However, whenever using the following code:

UdpClient whatever = new UdpClient(11000);

I always get a SocketException with any port number (not just 11000), unless I don't specify a port at all. This won't work for me because I need to have it specifically on one port only.

I've even copied/pasted the Microsoft example (http://msdn.microsoft.com/en-us/library/system.net.sockets.udpclient.aspx) into a new project and tried it, and it compiles fine but I still get a socketexception with no explanation when initialising the UdpClient with a port.

Any ideas? This is doing my head in...

From the same site you linked:

If you receive a SocketException, use SocketException.ErrorCode to obtain the specific error code. Once you have obtained this code, you can refer to the Windows Sockets version 2 API error code documentation in MSDN for a detailed description of the error.

It provides error 10022, which is a invalid argument applied - However, I fail to see how providing a port is an invalid argument.

I've even tried copying and pasting UDP server examples into new C# projects (to check if it's anything in my project at all), but I still get that exception/error on the UdpClient initialisation...

Sounds like you have a permission issue, either firewall or security settings on the machine.

I don't think it could be that - A Java server that I did a while back works (UDP on any of the ports I try), and disabling the firewall/antivirus didn't affect the C# server at all.

The problem persists for ANY port except 0, although it seems to work if I add an IP before the port in new UdpClient - However would adding an IP address restrict the ability to receive data from all clients connecting to that port (in my case, 11010)?

Okay, so I've upgraded to SP3 (Windows XP, was SP2 before), NET framework 4 (from 3.5) and Visual C# 2010 Express (was Visual C# 2008 Express).

Still no change, Error Code 10022. I've been searching online for hours and I've still found no solution - Every UDP server example gives me that error as does my own server.

EDIT - Ignore this, Connect is only for clients... Binding still doesn't work...