Master Pipe Connection Lock

When I try to start up Garry’s Mod I get this error:

SteamStartup() failed: SteamStartup(0xf,0x0028E418) failed with error 1: failed to take master pipe connection lock

I don’t know why its doing this, if anyone has any clue on how to fix this, help would be appreciated. Thanks in advance.

Restart Steam

(or your computer)