Welcome to the group finally, James! I am sure we will find someone who has come across this before (I sure haven't).
what's happen if you restart the TFTP service? (s. realtek problem... http://www.msfn.org/board/index.php?showtopic=61725)
Did you try a other free TFTP?
Did you check this: http://community.landesk.com/support/docs/DOC-1230