I routinely use unetbootin to test and install UberStudent editions. It works well. I'm personally a big fan of the application.
It sounds like the UberStudent ISO file you downloaded may be incomplete, or became corrupt. That occasionally happens while downloading it, for a variety of reasons. ISO file corruption is less of a possibility with the Lightweight Edition, because the ISO file is smaller and fewer things can go wrong. Getting a pre-made disk avoids the possibility of ISO file corruption altogether, if you wish to take that step.
So as a first step, please follow the steps to
Verify an ISO File for the installation ISO you downloaded, and please post back the result. Let's rule that issue out or in.
Also, since there are numerous UberStudent editions, please let me know the exact name of the ISO file you are attempting to place in to a USB drive via unetbootin.