Things you need to know how to do: You must know the difference between internal and external IP address

Answer:
First off, goto http://forums.srcds.com/viewtopic/7124

Still doesn't work? Or, already did that?

If you have the -ip or +ip command in there, get rid of it. However some people need it for RCON to work. What you probably did was use your external IP address so -ip (External IP), when really it has to be -ip (Internal IP). It's just easier to get rid of that command, but if you need it, use your internal IP.

Still doesn't work? Or, already did that?

Post in the forums.

What this error means is that the server can not find a connection to the needed UDP ports. This error is normally cause because of an incorrect -ip command. When the -ip command does it make the server use a connect with that IP address to host the server. If you list an IP that the computer does not have, it will cause a UDP error since it cannot use the ports on a connect it does not have.

In most cases a -ip command is not needed since it is meant for server with multiple IP addresses. If you feel inclined to use a -ip command, use the IP address that your computer has (aka Local IP). In windows this can be found with the command ipconfig at a command prompt.