Bruno
On the export side....
What version of Premiere Elements are you using and on what computer operating system is it running?
Please confirm what you want for export settings
Frame Size
Frame Width 1920 and Frame Height 960 pixels
or
Frame Width 960 and Frame Height 1920 pixels
and
Frame Rate, including Interlaced or Progressive
Video Compression/Audio Compression/File Extension/File Size
On the import side...
What are the full properties of this 16:9 file that you have on your Premiere Elements Timeline?
What project preset have you set for the project before importing your 16:9 file?
Please supply the above information, and we will customize a reply for you.
Thank you.
ATR