A little problem

There's a vertex in my wad that the error-check says is a duplicate. If I try to cut it out or delete it, etc. For some reason, before this error the level was fine -- but afterward, there were visplane overflows here and there on certain sectors unrelated to that vertex. What can/should I do to fix this?

Try removing that particular room and start over. I've had to do that a couple of times before. It's not fun, but it did work. Or you could just test it on ZDoom or other source port.

Once in a great while I get these and most of the time I can grab the offending vertex and drag it over to a new grid placement and all will be good. But I always try to delete a dup. vertex if found. It sometimes "confuses" the game engine.

Drag one of the vertices out and see what it belongs to - then decide what to do with it. (and the stuff it's joining)

Moving it should do the trick like Searcher said..

I may have to delete the whole darn thing. The vertex in question is all by itself -- there's nothing to move or to join to another vertex. : /

Job said:

I may have to delete the whole darn thing. The vertex in question is all by itself -- there's nothing to move or to join to another vertex. : /

It is probably attached to a zero length line with no textures on it. That could cause HOM and maybe even visplane over flow if there are other in the map. I would suggest you delete it if it is not attached to anything. Deepsea could do this for you if you use it.

I can not think of one reason you would want to keep a vertex that is not attached to anything.

Make a back up of your file and them work on the copy to see if it makes a difference when you delete the vertex.

If you don't use deepsea maybe someone you know could run their error checker over it and then return the map to you.