get an error anytime i try to play gmod

[omega52390]

this is a very strange problem that is only occurring in gmod. tf2 and left4dead work just fine but any time i try to host OR join a multiplayer game in gmod i get an error saying "Account used elsewhere" and it wont let me join same thing when i host but its only on one computer and its only on gmod

[ProboardslolV2]

Change your password, try again

[~Kiwi~]

Restart steam, 1 steam account can't be used by 2 computers at the same time it's impossible. So you above get a dumb box.