This entry is a user-made guide and not verified by any eMule developer, but is still a helpfull addition for most users. You you can find questions and comments on this topic in a dedicated thread on our forum.
A4AF means nothing else than: Asked For Another File
You can see this notification if you're trying to download two files from the same user. It's not possible to get these two files at the same time from this user because eMule will queue for only one file. That's why A4AF exists.
For example: Your waiting for the file A in the queue of a user but also want to download file B from the same user.
When you double click on file A in the transfer window a list appears. This list shows all sources for file A. Sometimes one of these sources has no queue rank but shows instead the message A4AF. This means you already requested from the same user file B in addition to A. If you don't change anything about that eMule will complete file B and then the source will be switched to file A.
eMule gives gives you the opportunity to influence these A4AF sources in one way only. You can right click on a download and choose a different download priority because eMule assigns sources for different downloads with the same source by this priority.