no dialog, lfroen:
"BUT, I don't know where it should be placed really. Either the Tranfers icon could turn into red or some different icon, or in the transfers tab some red (or visible colour) thingy should appear"
phoenix got the idea. I mean some visible change in GUI, in transfers tab or transfers icon. No dialog, of course, that would be disturbing when aMule is minimized, in tray, no-one-infornt or even when the user simply doesn't care if there's space for all files.