And how come when I make a regular ladder I don't get the 'no visible brushes' error?
Your supposed to tie the entity to aaatrigger, not to the clip brush...
And, because I was determined and didn't give up, I got the net to work. I got rid of the clip brush completely, and made the net part a func_wall. Then put the aaatrigger in front of it and made it func_ladder, and it works