Edit: Stojke beat me to it and is likely more helpful than my advice. ^_^
Does the point file show anything? It can help you trace out where the leak is.
Here is some info about finding and fixing leaks.I can't look at your map right now, sorry.
Here is a more manual approach if you are still confused about the point file or can't seem to find it somehow.
Do you know how to use the cordon tool?
Basically, it lets you draw a box around a section of your map, and when you compile, it only compiles what is inside that box. It can be very helpful.
So, use the cordon tool and draw a box over half of your map then compile. If the map doesn't compile, the leak is within that box. If the map does compile, it's within the other half of your map.
Just to be sure, cordon exactly the other half of your map. If neither half compiles, you do indeed have a mysterious leak.
But if you find that one half or the other compiles just fine, you can continue to narrow it down. Take the half that has the leak and cordon half of that and compile. Keep doing this until you can isolate a small enough section or a room that may have you leak and investigate that area. Sometimes it's small, sometimes it's a brush entity that is up against the void and a world brush needs to be placed.
Either way, I hope you find and fix your map. Good luck!