Occasionally the Photo Booth Upload software will detect an error in the current set up. There are a number off errors that can be detected and they will appear as a button at the bottom of the preferences page called Number of Warnings: X - Click for More info. Replace X with the number of warnings. It will appear like so:
When selecting the Warning, a pop up will appear that could appear like this:
Other errors include having the incorrect codecs installed for Photo Booth Upload. If this is the case, please click on this button and it will provide you with a link to: http://www.free-codecs.com/k_lite_mega_codec_pack_download.htm
On this page- download the latest pack. When your browser asks you what to do with the downloaded file, select "Save" (your browser's wording may vary) and pick an appropriate folder.
Install the codecs onto your computer by following the steps in the wizard, then restart Photo Booth Upload and you should be all set.