Comment 3 for bug 1397401

Sorry, I thought the automatically-filled details would give context, so I wasn't very clear in the description.

I know how to start the upgrade from 12.04 to 14.04, but when I do that I get the error message I pasted at the top of the description. I've amended the description to reflect this.

I tried the terminal command you suggest - it ran for several minutes with no visible output and stopped. Attempting to update after that still gave the original error.