"Only one Dota 2 per customer."

[Expresate]

Alright, so I played Dota 2 for a couple of hours last night, then logged off and went to bed. Now, today, whenever I try to launch the game via Steam I get an error "Only one Dota 2 per costumer." I've tried restarting steam, verifying the game cache, etc. What's going on? I haven't tried playing the game on any other computer, or anything. Any idea?

[Terin7]

That's appeared for me whenever there's another source game running. Open up the task manager and see if there's a hl2.exe running somewhere, or another source game. If you were able to restart Steam, none of those should have been open, but it's a place to start.