I am one of the owners of the TWC clan, which Sky is a member of. I have no doubt that he is getting falsely banned and tried to find out more about the problem. Here's what we did so far: used TeamViewer to control his computer set up a Silent mod server, all default settings ran the game and got banned on map change tried two different custom ET installers (one of which was downloaded from this forum) no custom pk3 files, our unmodified server was the only one these installations were connected to disabled anti-virus killed all userland processes except for TeamViewer, ET and a few processes from Windows itself We removed the ban between all of these tests respectively (some of the bullet points being several tests on their own). Surprisingly, when running ET Legacy we were able to connect to the server and get into the game perfectly fine. While we cannot currently identify the problem, we can definitely reproduce it 100%.
Unfortunately, the server wouldn't show anything more than a message like "banned for technical evidence of cheats". I assume there is no way to find out what that evidence is for security reasons? If that is the case, I'd like to know what we can do to help you identify the problem so that it can be fixed eventually.
While we don't run a Silent mod server for our clan we'd like to help solving this issue to protect the reputation of our member(s).