How do i stop the window catch fouling the frame?

i have an up and outward opening upvc window but the catch is fouling the frame.
it seems to have evenly dropped and started to wear a groove at the edge of the frame. it seems fine in the summer and the opening casement has been previously adjusted by a window fitter but the problem has come back.
i was thinking of tidily exagerating the groove with a sharp chisel as i think that this would cure the problem.
Any Help please??? desperate now ;(