I just had this happen, heres how I got around it, not sure if it was the correct way or not but it worked. I will say after it got booted i got rid of that rom and put another one on.
Pull the battery and do a reset. Hold the volume down and power button to boot up. You will go into the bootloader and it say there is an upgrade. Volume up to select yes, it will go through that then say hit power button to reboot. Reboot and while it is booting up I kept hitting the volume up key during the whole sequence. Once it gets to the 4G screen keep hitting up, it should hang for a little on that screen then it will go into an install saying loading 1 of 74 updates or something like that. Once that finishes it should work.
I also at one point had to pull the SDCard during the boot and do a wipe/factory reset to get it work but only one time.
Not sure if it is us messing up the install or the ROM itself but I am now using RezRom ICS and it installed without a problem and it seems to be running smooth. Only some minor glitches so far but I had no luck with with the Senseless ICS