FPS drop, "does not support higher settings"

Hello
I recently came back to Heroes after about 3 years break and though I was able too play this game on high graphic setting before I now see “does not support higher settings” in the option (but game suggest all settings on high).
In-game I have 60-70 fps most of the time but in team fights it drops to 0-20fps. I updated my drivers even set graphic settings to low but this didn’t help.

Intel i5 CPU 750
4Gb RAM
GeFroce GTS 450