After booting Ubuntu 13.04 for the first time via USB, having not even installed it yet, I get the following message:

I previously dual booted Vista with Linux Mint 11. I am now locked out of Mint! I didn't even install Ubuntu or give it any commands but to boot from USB! When I try to login to Mint (which now looks different at the login screen), I get this message:

Here is exactly what I did step by step that created the issue:

1. Downloaded and Installed Linux Live USB Creator 2.8.22
2. Using the above program, I selected Ubuntu 13.04 to download onto my 32GB Kingston DT101 G2 USB stick. (It did detect that my USB was FAT32)
3. I completed every step from download to installation onto the USB until it told me the USB was ready and I could go no further.
4. I switched BIOS to boot from USB (which it considered a second harddrive).
5. Upon booting, the Ubuntu load screen became visible, but stayed there for a very long time.
6. After waiting for a long time, I decided it was frozen. I tapped enter (and maybe a couple other buttons) and it went to a black screen that it did not recover from after much waiting.
7. Restarted computer while booting from USB again. Ubuntu load screen appeared again, but was followed by a black screen with the message I gave at the beginning.

I can go no further with Ubuntu 13.04 after that, as far as I can tell. As is obvious, I did NOT install it onto my system yet -- I simply tried to boot from USB -- but it somehow destroyed my Linux Mint already...

Should I just download a different OS onto my USB and try again? I'm extremely disappointed in Ubuntu 13.04. That was definitely the version I wanted, but clearly it's buggy.

Go back into the bios and change the boot priotity back.

I did. That's how I was able to get onto windows and attempt to get on to Linux Mint. I spent 2 days on the issue and couldn't find a solution, so I installed openSUSE 12.3 instead and I am pleasantly surprised with it. Nevertheless, I am still curious as to what the problem was because my girlfriend has been eager to install Ubuntu 13.04 on her machine as well when she gets back from a family vacation (she thinks the unity design is beautiful), but she has no experience installing an operating system. So, I think I may have to tackle the problem one way or another.

I am not a Ubuntu user (I use Slackware), but someone else I know had trouble installing updates to Ubuntu, gave up, and dumped the Ubuntu disks on me because it was all locked up.

Sync error and Panic. Sounds like it could not establish logging files to disk, or could not find disks. Long waits are almost always stalled I/O access to disks. Would have to find those error messages in the kernel code to really know what it was doing that failed.

The same thing happens if you create an ISO image on a CDROM of a Linux that is setup to boot from disk. It cannot write to the CDROM which is the default root !

Might have to create an initRAM boot, which will give it somewhere to log.
Otherwise where does it write log files, back to USB ??
But USB write access is usually not complete in kernel, like the root filesystem disk access. It usually involves modules.
The root disk hardware access and the root filesystem must be complete in the kernel that you are booting, without using modules. For strange hardware setups, this may involve creating a custom kernel. Otherwise boot a kernel image with initRAM as the root filesystem.

In addition, make sure the new Ubuntu install cannot see nor find any existing Linux installation. Rename everything to hide it.
This will require a CDROM linux boot to do, and to undo afterwards.
It then cannot get confused by finding existing files, and cannot destroy the existing install. Installs behave differently when they find existing files. Real confusion when they find files setup to use a different directory organization.
Each Linux configures the directory structure differently.