It seems like we have Premiere Elements 12/12.1 user presenting with the same type of MPEG2 export message
Please check out the questions that I have asked of that user.
In your situation....
What are the properties of your source files on the Timeline?
What is your project preset?
What is your export choice
and then what have you selected under Presets. After you make your choice of the preset, are you using the Adobe default settings for that preset or are you customizing the preset under its Advanced Button/Video Tab?
Do you have the latest version of QuickTime installed on your computer with Premiere Elements 9? Are you running 9 as the 9.0.1 Update?
What is the Save In location that you have designated in the export dialog in the Share route?
Let us start here and then decide what next.