I tried again with the small stripped kernel, and using tcpdump.

The (FreeBSD) tftpd reports success and tcpdump shows this:

15:29:50.365164 hawk.dbnet.ece.ntua.gr.1228 > thira.dbnet.ece.ntua.gr.54119: udp 516
15:29:55.368912 hawk.dbnet.ece.ntua.gr.1228 > thira.dbnet.ece.ntua.gr.54119: udp 516
15:30:00.378939 hawk.dbnet.ece.ntua.gr.1228 > thira.dbnet.ece.ntua.gr.54119: udp 516
15:30:05.388999 hawk.dbnet.ece.ntua.gr.1228 > thira.dbnet.ece.ntua.gr.54119: udp 516
15:30:10.399058 hawk.dbnet.ece.ntua.gr.1228 > thira.dbnet.ece.ntua.gr.54119: udp 516

(hawk is the tftp server, thira is the 5k/240).

However, this is the last error I get from the 5k/240

kernel not configured for systype 0x82040230

Ideas anyone?