Performance problem

I have a strange problem.

I am trying to make a change using GP4Tweaker, specifically the "jump start realism enabler", yet whenever i do this it renders a race unplayable, it turns it into a slideshow.

During qualifying or practice the game runs perfectly normal, yet the race as i said, turns the game into a slideshow, absolutely unplayable.

I'm assuming that because i'm making a change thats related to the race itself, thats why its affecting only the race but not practice or qualifying.

I have deleted the F1Graphics.cfg and let the game create a new one, which didn't solve the problem.

I have played with different texture settings within F1Graphics yet nothing.

I'm stumped, what on earth would cause this to occur?

I have a high end computer which can easily handle GP4 so thats definitely not the problem.

Thanks.

Slasher.