What version of Premiere Elements are you using and on what computer operating system is it running?
How many times today or on other days did you attempt upload your Premiere Elements Timeline to YouTube from within Premiere Elements and got this message?
What is your project preset? And, what are the properties of your source media on that Timeline including duration?
It would be advisable to determine if you can export that Timeline to a file saved to the computer hard drive and then upload that file from there to YouTube at the YouTube web site and see if that succeeds.
If we knew more details about your Premiere Elements version and project, we could be more specific, but that suggested file for upload at the YouTube could be a H.264.mp4 from version 11 Publish+Share/Computer/AVCHD with appropriate preset (also, export settings could be changed under the Advanced Button of the preset selected).
The answers are in the details.