It seems that when using Friend Slot, then there is severe problems for aMule to make a connection to the client which got Friend Slot.
If a connection is already created between the clients (a message has been sent in the messages tab, or the other client is already uploading to me), then FS works fine, but if no connection exists between the clients, then it seems like aMule "forgets" to connect to the other client, but thinks it has. The other client still thinks it is in my upload queue, but the client is in my upload with a "Connecting" status and after a few minutes, the client is dropped from the queue.
aMule can still ask and reask the other client for new downloads, but will not upload.
This has been happening as long as i can remember, so it's not a 2.0.0-bug, actually ISTR it happening back in the xMule days...
