When I ran glvis -f doom2.wad I got the following error message: Leaf portals saw into leaf. The wad compiled into a .gwa file without<br>any errors before & I did not change the wad in anyway. What does the error message mean? & How can I fix it? Thanks a Mil.

It means that subsector can see itself which theorethically is impossible. This can happen with version 1 of the GL-Nodes. You should rebuild .gwa file using latest version of glBSP