How does auto-grant slots feature work?
There are 3 extra slots (apart from those you specified in settings) that will be used for uploading files under 64KiB and for uploading your filelist, no matter the size. Operators in the hub can download mini-files and filelists even if those 3 extra slots are full. In DC++ versions later than 0.671, the mini-slot size is configurable for anything larger than 64 KiB. This is the reason that you can download some people’s filelists, but when you try to download a different (larger) file, you could get the “No slots available” message. All recent DC++ clients should allow the filelist to be downloaded. If you receive “No slots available” or “connection closed” right away, it’s very likely the user is slot blocking. Report them to a hub operator.