Can download and receive uploads but can't upload to specific users with open upload slots

Hi, I'm running SoulseekQT on Linux Mint...took some doing but I got the port forwarding set up properly so that people can upload off me (and I can download no problems) but I can't upload to specific users who have open upload slots. I always get a "Cancelled" status even from people I know I should be able to upload to. Is there a specific port I've missed that is separate for this function? My username is coaxihuitl...