I am using lighttpd and am randomly receiving the message in our log "Server closed socket during multipart read (client aborted?)". This happens with files of any size, including 50kb. The oddest part is that I can't reliably reproduce the bug. If it fails, the 2nd time it might succeed (or maybe the 3rd, or maybe the 4th, etc.).

I can't point fingers at uploadify with 100% certainty, but it seems like the most likely candidate for the source.