From the Premiere Elements Information FAQ http://forums.adobe.com/thread/1042180
•What version of Premiere Elements? Include the minor version number (e.g., Premiere Elements 9 with the 9.0.1 update).
•What operating system? This should include specific minor version numbers, like "Mac OSX v10.6.8"---not just "Mac"
•Are you using an account with Administrator Privileges?
Run as Administrator http://forums.adobe.com/thread/969395 (Encore + "All" Premiere)
•Have you installed any recent program or OS updates? (If not, you should. They fix a lot of problems.)
•What kind(s) of image file(s)? When talking about camera raw files, include the model of camera.
•If you are getting error message(s), what is the full text of the error message(s)?
•What were you doing when the problem occurred?
•What other software are you running?
•Tell us about your computer hardware. How much RAM is installed? How much free space is on your system (C:) drive?
•Has this ever worked before? If so, do you recall any changes you made to Premiere Elements, such as adding Plug-ins, brushes, etc.? Did you make any changes to your system, such as updating hardware, printers or drivers; or installing/uninstalling any programs?
And some other questions...
•What are you editing, and does your video have a red line over it BEFORE you do any work?
•Which version of Quicktime do you have installed?
What version of Premiere Elements are you using and on what computer operating system is it running?
What is the exact wording of the error message that you are receiving?
Where are the Video Previews directed according to Expert workspace, Edit Menu/Preferences/Scratch Disks and how much free hard drive space is at that location?
If you are still working from default locations, how much content do you find in the Adobe Premiere Elements Preview Files Folder in the version number Folder (path: Libraries/Documents/Adobe/Premiere Elements/version number)?