problem with enet on 3C120 dev board

To recap the problem:

- I have two (supposedly) identical 3C120 dev boards, one purchased 2008, one in 2010, with all jumper settings the same.

- The standard "Simple Socket Server" program runs fine on both boards.

- My custom program based on SSS works on the old board but not on the new one. They compile and start up identically, but the new board freezes immediately after the typical uCOS/iNiche messages.

New info:

- The new board actually does not freeze at "Checking Link" - it makes it past all the same setup messages code as the old bd, but freezes before the printf() screen can finish updating.

- After carefully stepping through the code (to give printf() time to finish), I get the infamous message immediately before the freeze:

"no free buffers for rx"

So then the question becomes: what dev board change could possibly create a "no free buffers for rx" problem? The documentation certainly doesn't mention any bd changes. Is anybody here smarter than my Altera field rep that couldn't figure it out?