Go into your launch options and add +mat_dxlevel 95 into it. If you use an autoexec, you can put it in there instead. Make sure you are not using any -dxlevel launch options and that you are not using mat_dxlevel 80 or mat_dxlevel 81. The error has occured for me when using DirectX 8.1 and DirectX 8.0 and I'll presume that continues to be the issue.