Welcome to the forum.
Can you tell us what version of PrE you are using, and on which OS version?
Then, please let us know more about your Project settings, the full specs. of the video on your Timeline (Imported into the Project), and exactly what you are doing, when this problem occurs.
Thanks for that info, and good luck,
Please verify that you are using Premiere Elements and not Photoshop Elements?
What feature are you working with in the program that is involved?