The GUID is basically means your STEAM ID. What you want to do is join a server, any server. Open your console, ~ , and type "status".
A list of names will come up of everyone in the server. Next to youur name, you will see this: STEAM_X:X:XXXXXXX X X ACTIVE. (at least something close to that)
All you need is the X:X:XXXXXXXX (the amount of X's after the second : varies)
On your TWL profile page you will see In Game Anti Smurf Identifiers. Right under that you should see "Add another ID". Click that.
Select STEAM ID from the drop down list, add the X:X:XXXXXX and click add ID. You may now join a team/ladder.
EDIT: I see you attempted to enter the steam ID already. From the looks of it, I don't think you did it right, and neither did your teams founder. Consider revising it. I have seen suspensions handed out for that. Post edited by snizz. at 11/8/2009 3:10:21 PM