Cry-tek Posted earlier that you need to UNINSTALL MP DEMP after you have done that fine where the DEMO FOLDER was and delete anything that uninstall missed. After you do that UnInstall the Full Version of C2, Then ReInstall (you might need to select a different drive to put it on) Then Patch to 1.1
If everything goes will since you didnt delete the .cfg file from the Full Install you should still have your Serial Key saved as well as your MultiPlayer access login info.
What is happening? MS Registry is calling for info and its looking for it in the MP Demo Folder and the Info simply isnt there, and it needs to be redirected to the Full Version. Do this by following to the letter whats stated up top. It Should/will Solve your online disconnection problems.
Please Note I still have all the ports open for GameSpy and whats found in the Book that came with the game.
For the Serial Key problem: Click Modify and delete it re-type the key using all UPPER CASE numeric and alapha numeric keys and DO NOT USE ANY DASHES (IE: - )