You posted in the wrong (this is the Premiere Pro forum), but a moderator will come along soon and move it to the Elements forum.
Any way avi is a container also called wrapper. Its the codec that is inside that determines whether or not it will be supporte.
Run a file trough mediainfo and post a screendump of the analysis pref in tree view
[moved to Premiere Elements forum]
Welcome to the forum - the right one now. Thanks Jeff.
As Ann points out, an AVI file can contain a lot of different material inside that "wrapper." Some will Import and edit perfectly in PrE, but some will not. This FAQ Entry goes into much more detail, and also suggests that file info utility, MediaInfo, that Ann posted the link to: http://forums.adobe.com/thread/440037?tstart=0
If you will let us know the full details of that/those AVI file(s), we can advise you as how best to proceed.
I had the same problem. It was solved when I installed Quick Time. Try it!
What version of Premiere Elements are you using and on what computer operating system?
I do not see the rationale behind the QuickTime (latest version) resolving your issue specific to a specific MotionJPEG.avi based issue.
If this is a MotionJPEG.avi issue, then
a. you convert the video to another format that is compatible with Premiere Elements on your computer operating system
b. you install the Morgan MotionJPEG codec
even if the gspot readout says "codec installed".for the video codec.
If you give the properties of this MotionJPEG.avi (frame size, frame rate, aspect ratio), I can suggest a format to which to convert the MotionJPEG.avi for your projects.
Taking your MotionJPEG.avi out of the equation, the installation of QuickTime and running Premiere Elements from a User Account with Administrative Privileges have always been part of the system requirements for the program.
If you have not already, please rule in or out whether installation of the Morgan MotionJPEG codec will resolve your issue.