Have a read of this:
http://forums.techguy.org/8441011-post3.html
It may be that some deeper repairing is needed.
The "gotcha" here is that it works directly connected to the modem. Maybe it's the ethernet cable - like it's a crossover cable that the olsd modem handles nicely and should be replaced with a non-corssover cable.
Straws really. I'd fix it if I had my hands on it!