[ubuntu] 13.04 upgrade. error: file not found

I ran the upgrade to 13.04 on a System76 laptop. When I boot I get

error: file not found
error: file not found
error: file not found

press any key to continue

After pressing a key, the laptop boots and runs fine.
I have not been able to find a solution to this problem.

It would be very helpful if the messages would tell me what file can't be found.

So far I haven't found anything useful in the logs, but I may not be looking in the correct one.