The Big Block MethodI guess TWHL doesn't have any tutorials on leaks? :
If your level is especially large and you're having difficulty tracking down your leak, you might benefit from using the "Big Block Method" of leak tracking. What this is essentially, is you covering a large portion of your level with a solid block (make sure it goes completely through from top to bottom). A recommended size is a quarter of your level.
Place the large block over a portion of your level, then attempt to compile. Move the block to a new section and recompile until the leak error disappears. When this happens, you know the leak is somewhere within the space of the block. Now you can repeat the procedure using a smaller block, only within the space that was covered last with the big block.
This method would only work, of course, if you had one leak, or a number of leaks that would all be covered at once by the block.
Is there any other reason why it would be saying there is a leak?Well, this is just a guess, but... I'd say you might actually have a leak.