Needing help with Gmod

I get an error message when I try to join a game:
“Account used elsewhere
This Steam account has been used to log in from another computer. To continue using Steam you need to log in again.”

I restarted Steam a couple times when I still got the message so…
There is no way someone is logged on with my account, because every other Steam’s game works perfectly. I would really need help ASAP.

Bump

restart your computer

Log out and back into steam.

Goto the Steam browser thing (where library and the store is) and click Steam, then change user and re log in.

Odd.
I had this sort of problem before, and it wouldn’t fix like it usually did.
My solution (Oddly enough), was that I had logged in on my laptop (Which was actually off).
I had to start it up, and log off on the computer (It automatically logged in).
After that, it worked.
No guarantee it will work, just a suggestion if all else fails.

Wow, I seriously had to log-out from Steam browser…

that should have been the first thing you did

Well I exited Steam and logged back in but that didn’t work.

What Zelerdood said. (Remove clientregistry.blob and restart steam)