You have a bad brush or a bad patch. It could be caused by tons of stuff, but basically you did something that Radiant didn't like. Radiant is old and cranky and you have to it right or else it gets angry!
Try some of these:
- TEST: Open your map. press "i" to select everything. In the z-window (all the way to the left of the screen), keep scrolling up or down to see if there is an end of your selected brush. If there is no end no matter how far you scroll.. you got a brush without bound. FIX: One by one select your brushes and hide them "h". once everything is hidden, press "i" and it should select the brush without bound. Press delete.CAUSE: Modifing vertices can confuse Radiant, and radiant lost one of your verticies.
- TEST: Look around your map for tiny tiny tiny brushes. FIXIf you find some, delete them. CAUSE: CG subtract is the most evil feature in Radiant. Don't use it...
- TEST: Temporarily delete all your patches in your map. You might want to make a copy of your map. Compile your map and see if you get the error. FIX: if you don't get the error then you know that you have a bad patch. One by one copy the patches back into your map until you get the error. Delete the last patch and re-make.CAUSE: same as #1, radiant inconveniently losses verticies.
- Worst case: copy your map section by section one at a time into a new map file. Compile each section until you get the error. Then you know what section has the error.
These errors are very typical for beginner mappers. CG subtract is the root of all mapping evils, and new mappers don't know the limits of moving verticies. Only time and experience can reduce these. I say this, but I had to delete a large section of Comanche canyon because I was getting a runtime error!