Arrgh, these cards !!! I am building a server for a school (first one I have done for someone else) and have been through 4 different cards in 2 hours (had 2 realtek 8139c's working fine, then plugged in another box and bam ! lost one card !!!).
Anyway, I swapped in another identical realtek (after trying some other cards , including tulip chipset @ nci.nk (or somehting like that)) and back up and working again. The only problems I have ever had with e-smith were with network cards suddenly deciding that working was no longer part of their mandate. They would show up for selection in the console, and even appear in ifconfig and would be pingable but would NOT work. I spent 2 hours last night stuffing around with cards..grrr!!!
Anyway, end result is that if one card does not work, swap in another and see if that does work...no rhyme or reason, just the way it is