V sync Horizontal flashing line issue

[jd802]

I accidently put this in the zdoom forum but Im having a problem when im in opengl there is a horizontal line that flashes when running and it makes the graphics on the walls not line up I have no idea whats causing this but when i turn v sync on this happens I have a radeon 9200 video card.

[doomexpert]

your videocard, you must have both v_sync and anti aliasing option. those must working together i think