When I tested 1.20 with Hexen, it gets an error making the vis data.
It makes the gl nodes ok, using either vavoom or the gl bsp program, no errors there. The problem happens afterwards when it tries to make the vis data, using vavoom with its fast mode, or the gl vis program, it will crash on the first map saying "Leaf portals saw into leaf".
This happened with my old hexen wad that I had used before with vavoom, so I deleted it and recopied the wad file off my original hexen cd. The error still happens.