It is always important to give Premiere Elements version and computer operating system involved.
But, I think that I know what you have run into, and it is the persistent Videomerge effect.
Some history on its activity can be found
But here is what I want you to do
1. Go to Expert workspace, Edit Menu/Preferences/General and place a check mark next to "Show all do not show again messages".
2. In the Expert workspace, use Add Media/Files and Folders/Projects Assets to import this video. Drag the video from Project Assets to the Timeline.
3. In the Videomerge pop up that I expect you will get, put a check mark next to "Do not show again" and then click No.
That should prevent a reoccurance of the problem. But, be on guard for a reoccurance when you least expect it. Just reapply the fix. You know what to look for now.
Please review and consider the above, and let us know if the above worked for you. Need clarification on any of the above, please ask.
Thanks Romano. Any feedback on the flickering I'm getting on the video (my second question)?
For information, I'm using The latest version of Premiere Elements (13?) and Windows 7 Professional
I am suspecting interlaced - progressive issue. But let us look at the details.
1. You have a video file with a .mov file extension. Is the frame rate progressive or interlaced? What are the properties of this .mov file....1080i or 1080p or something else?
2. What are you (manually) or the project (automatically) setting as the project preset to match the properties of this source? If you are not sure, please tell us what the readings are for Editing Mode, Timebase, Frame Rate, and Pixel Aspect Ratio under Edit Menu/Project Settings/General.
3. Have you taken the Timeline with this .mov to export yet? If so, do those lines appear in your export choice?
Let us review the details of the above and then decide what next is indicated.