It's hard to say without knowing more specifics. Are you able to upload a short, 10 second video to YouTube?
Can you use Publish & Share/Computer/AVCHD with the YouTube HD preset to output a video and then manually load it to YouTube?
What computer operating system is your Premiere Elements 12 running on?
How do you upload content to YouTube
a. For 12, Publish+Share/Social Websites/YouTube which preset
b. For 12, Publish+Share/Computer/and a choice such as AVCHD to export to file saved to the computer hard drive, followed by uploading that saved file to YouTube at the YouTube web site.
How far do you get in the process? And when specifically in that process does the error appear? Have you tried "a" and "b" cited above? Does "b" work while "a" does not.
What exactly is on the Premiere Elements Timeline in the way of content and content duration? Are you over 15 minutes in content duration?
Please supply the above information and let us know if "b" as a troubleshooting tool works for you.
Welcome to the forum.
What does that unhelpful error message say, specifically?