Is it a yellow or red color?
If so, that's likely due to your footage and the software not communicating quickly enough so you're getting "missing media" or "media pending" screens. Where is the footage located and how is that drive connected to your computer? Also, what are your computer's specs?
I agree with Michael. You've got a stray missing clip.
Zoom into your timeline and you should see it (though you may also have to check on an upper video track.)
What version of Premiere Elements and on what computer operating system is it running?
What is the brand/model/settings of the camera that recorded the Timeline source video? Are all the clips on the Timeline from this same camera?
Please expand the Timeline with the -+ slider above the Timeline. Inspect each of the clips on that Timeline and note which ones have the colorful display and which ones do not. Do you see an obvious difference between the do and do not? Do you recall moving, deleting, or renaming any source files and folders that were imported into the project after the project was saved closed. When you import media into the project, all you get are copies of the originals which have been saved to the computer hard drive. But the project copies need to trace back to the originals on the hard drive location where they were when they were first imported into the project.
After you save, close, reopen this project, do you get "Where is the file ______?" message(s) that you need to answer before the program allows you to continue - unless you opt to use Skip All to enter the project?
By any chance have you incorporated your video clips into an Instant Movie named Outdoor Adventures? If so, please refer to
Are all the Timeline clips (project source media) stored in the same place (like an external hard drive) on your computer. If so, the would tend to take the focus off an external hard drive malfunctioning or drive letter change.
Please review and consider the above. We will be watching for details from you to help us help you.