Shader File not Found when Shift Walking

So I log on to play with a few of my friends in a GP Guns only match. And you could not guess what happens next... I try to sneak up on someone Shift walking and CF Crashes saying Shader File not found.

Tried logging in a again and trying to play and yet again walking causes me to error.

This has happened 5 times so I think I got it narrowed down to Shift Walking along with Tab or W Keys. Anyway to fix this issue? Please help. I walk a lot and today is the first time I have noticed the problem. Also happens while Crouch walking and/or Tab.