i got these kind of errors several times, solved them, but forgot how
-disable visgroups all except world and areaportal, then compile, might get clearer that way
-see if the areaportal touches and doesn´t overlap or overstand on any side
-such an error could be due to another leak somewhere else, i think that was the solution to my problem, exchange the areaportal with a worldbrush for testing, and see if there is another leak