I fixed mine the other day using a 1.1.3 Doctor, but I don't expect OP to have that version lying around.
Originally Posted by sketch42
More info (copy):
Please note I stumbled across this fix when trying a 1.1.3 Doctor, a version you may not have.
Rod just told me this procedure "does much the same as what our recovery page says for a filesystem check boot loop". I'm checking with him whether the same applies to the 1.4.5 Doctor.
Answer: "maybe not, since by then they were attempting to preserve usb drive contents"