Client addons don't work on servers anymore.

Recently I have been using a radio streamer called “Aarrons menu” till it broke, then I tried using an MP3 player that once did work on Multi and single. But now the MP3 and radio client addons cannot be opened while playing multiplayer. I get the error “Unknown Command”. But when I go to single player it works. It also says that the addons are installed in the Extensions menu.

Why, And is there a possible way to fix this?

Well, it could be ScriptEnforcer or the addon needs to be on the server for it to work.

Never-mind, I fixed it. After I cleaned out my gmod.