I have never come across this error in Hammer before. All of the textures I have used before on test maps, and they have been fine. Though for some reason I keep getting this error.

materialPath: c:\program files\steam\steamapps\common\portal 2\portal2\materials
Loading C:\Program Files\Steam\steamapps\common\portal 2\sdk_content\maps\sp_safety_cube_v1.vmf
ConVarRef gpu_level doesn't point to an existing ConVar
Brush 314: FloatPlane: bad normal
Side 2
Texture: METAL/BLACK_FLOOR_METAL_004A

How do I fix this?

chickenmobile wrote:
Press Ctrl+Shift+G and type 314 into the pop-up then enter. Then delete the brush.

Thanks for that useful tool...had no idea about that. It pointed me to a slanted surface I made with the vertex tool.

Vordwann wrote:
How was it slanted?

I created a cube, and then used the vertex tool to cut half of it away, leaving a slanted side.