Mac Killing floor won't start up

[GameChanger]

Every time i want to play killing floor its starts up with the box screen then it disappears then after a few seconds it says on steam synchronizing game then it stops i don't know why it does this now but i have been trying to fix this problem for almost a month now

 

[SkullFinder123]

Try verifying your integrity. Looks like the initial install didn't completely work right.

 

[GameChanger]

i try that but the same thing keeps happing again and again it really gets annoying

 

[SkullFinder123]

Have you contacted Steam Support? also try deleting ClientRegistry.blob then restart Steam