I tried to update my TB and ran into the same problem. My TB was stuck in an endless cycle. After reboot, it would power down and try to install the update. The update would fail; the triangle with the exclamation point would appear. After the battery pull, the same process would occur. Thankfully, I back up my TB with ROM Manager. I restored the last backup and the phone is working again.
Here’s my question. I want to keep my TB rooted. Is it possible to update a rooted TB? If I un-root and update, will I be able to toot again?