I recently installed Ubuntu onto a USB drive and it was working perfectly. Today I tried booting from it like usual and it hung on the splash screen with the 4 little dots. I hit F8 to see what was going on and saw this:

http://img39.imageshack.us/img39/7779/imag0056yp.jpg

I made sure that the drive had been removed safely from windows and that my hard drive had been correctly unmounted when windows shut down. I really need to get this working because it has some code on it that I was developing that I need to finish since it's due soon.

I had a similar type of problem on a persistent SD flash card install. It happened that too many writes were done to flash.

I fixed it by plugging in the flash drive to one of my working linux boxes. Open gparted to look at the flash drive. Gparted showed the flash drive was full.

I right clicked on the flash drive in gparted and selected check from the menu. Clicked apply. It ran a chkdisk on the flash drive and when done and did a rescan. The drive showed 1/2 full. Then I was able to boot the drive again. The errors sometimes happen when a power dip or incorrect power down with flash drive is inserted which causes the file system to get errors. Hope that makes sense. Saved me time from doing a reinstall.

Thanks for the reply. I tried that and got a new error:

mountall: connection is closed

Alternatively, is there a way to recover files from it? If I can get a couple files off of that drive, I can just reformat and reinstall Ubuntu.

Got two USB ports and a second (good) USB flash drive with Linux on it? If so, and you did a full install, boot from the good drive, plug in the bad one, and run fsck on it. Not sure what your options are if you did a live install. With Fedora, in my experience, if the overlay file fills up, its a total loss.