What computer operating system is involved? Have you updated 12 to 12.1 using an opened project's Help Menu/Updates. If not, please do that.
But, to the immediate issue. My first impression is that you have a problem with your project and/or export settings.
Consequently, please supply details
1. Project Preset
2. Properties of Source Media
3. Export settings...to where are you uploading your Premiere Elements 12 Timeline and with what settings? What is this viewable format?
Once we have those details, we can develop some troubleshooting strategy.