We recently encountered a problem with our Ubuntu servers were they would boot up to the login screen, and continuously display an error where tg3_stop_block timed out.┬á After a bit of searching I found that tg3 stood for tigon3, and was the nic driver.┬á This wasn't an issue in 11.04 (11.10 on the servers), so I checked the driver versions for tigon3 between Ubuntu 11.04 and 11.10, and 11.10 had a slightly newer version.┬á Also the tigon3 driver was inherently part of the kernel, and broadcom wasn't offering any sources/ debs.┬á So a rollback was out of the question.
I continued to research this, but didn't have much luck diagnosing the problem.┬á So eventually we just decided to see if it was an issue in the 12.04 beta.┬á Oddly enough during the first install of 12.04 the installer prompted me for a tigon3 driver, so I looked around and found one on the dabien website.┬á I have a feeling the driver I found was old/ not for Ubuntu, because when I tried feeding it in, my install corrupted and I had to start over.┬á On the second attempt I skipped the missing drivers, and it installed flawlessly.┬á The stop_block error was also gone. When I checked, the tg3 version was newer, so it seems the issue was fixed between 11.10 and 12.04.
Turns out the solution was kernel related... Ubuntu 12.04 comes with a stock 3.0.23 kernel and herein lies the problem. I explained the details on the askubuntu.com stackexchange on how to fix the problem (hint - just upgrade your kernel (apt-get dist-upgrade))