Garrys Mod Error

When y play singleplayer in any map, the game crashes and a window appears. It say something like Debug Error!
Here’s the log:
[0911/180703:ERROR:backend_impl.cc(902)] Critical error found -8
Can anybody help me?

This is believed to be an error related to gfx cards.
Update your drivers, then check if it works. Try disabling steam overlay, turning down settings, but most important of all,read the FAQ.

But Garry’s Mod works to me in a lot of occasions,that’s the first time i see the error.
How i disable Steam overlay?

Steam settings, under the in-game menu. Should be something there.

Problem solved!Many thanks guys!