I got this strange bug on Ready2Roll server for about 15 minutes - there were red or grey/white walls or pylons in some plces on track. Then it disappeared I just wonder where to find guilty Could it be from server side (that was only on my installation), my LFS deep hacked or some graphic bug?

Was your GPU temperature ok or was it overheating?

I dont have CPU temp on my usual diagnostic set (and it shouldnt go up with no reason) - why you ask?

Well it could happen because of a graphics cars overheat.

Well, I've never heard that graphic card overheating can cause creation of 3d walls and pylons you can drive around

The problems caused by GPU(graphical processing unit) overheating are named "artifacts".They are usually just images. I had some of those but I would just drive through them.

Simply install lfs again