Sounds like you have the same issue that the Atrix has. Here is some detail on what is happening
On the Atrix, when the OTA update installs, it checks some of the system files and their integrity to make sure the phone is still stock. As the OTA installs, throughout the update process it checks different system files and their md5 hash numbers; if a file was edited (like in the webtop mod) or not the original file (replaced from someone else's phone), than the md5 will be different and the check fails, or if the file is missing it fails all together. The issue here is since the update has already been running and changing things and that once it fails a check it stops and crashes, the update was partially applied before the update stopped and crashed, so the phone becomes a brick. SO you want to make sure you are 100% stock or at least all of the original files are there before you run the OTA update
