I'm having the same problem with that card here on a Dell Latitude CPi A running Debian potato with a 2.2.13 kernel and cs 3.1.4. In the past, I had the ethernet part of the card working fine, but the modem was broken. After several days of tinkering, I got the modem to work, and at the time I did not need the ethernet. Today was the first time that I needed the ethernet again.
As the machine starts up (or when the card is inserted,) everything is fine (no errors are reported) until an attempt is made to send over eth0. At that time the following errors start appearing in /var/log/messages:
eth0: Transmit timed out, status 60660000, CSR12 000000c2, resetting . . .
which appears over and over again. If I ping for a long time (> 20 seconds) I will eventually get whole slew of replies all at once, usually right around the time the error message appears in the log. Judging from the card's network activity light, it looks like the card is not sending each individual ping. I have also noticed the machine with the card does not respond to arp requests in a timely manner, either. This does not appear to be purely a shared irq problem because I have the same symptoms regardless of whether the serial driver is loaded or not, and anyway I think irq's are used for more for receiving, not transmitting.
I'm backing out all of the changes that I made to get the modem to work in an effort to get the ethernet operational again, but I've not yet had any success.
The receiver part of the ethernet interface seems ok, because tcpdump works fine and sees the network traffic, if I have name resolution disabled.