What is the computer operating system on which you are running Premiere Elements 7? What is your export preset under Share/Personal Computer/MPEG?
What is the duration of your Timeline, and, before you hit the Save button in the export area, what do you see for file size and duration at the bottom of the export area?
Do you have the latest version of QuickTime installed on your computer with Premiere Elements 7?
Are you getting any error messages about MPEG2 Encoder Activation? Or, is the "failure to return a video frame" your only error message?
But when all is said and done, the probable cause of the issue will probably go to an irregularity in the Timeline content...a video gap...a fragment. You need to expand (to the max) the Timeline content with the -+ slider above the Timeline and look for such flaws in the Timeline content and remove them. Look for fragments that present as very thin black vertical lines scattered among the tracks content. Check all the tracks that are there even if you have not used them yet. A fragment or a thought deleted clip may be sitting there.
Please update us on your progress.