Wbat operating system are you using? How fast is your processor and how much RAM do you have?
Have you ensured you have the latest version of Quicktime?
What happens if you use Premiere Elements' Add Media tools (the Video Importer) to get the media from your device?
What are your project settings (under the Edit menu)?
I'd recommend you create test footage, then, and seeing if your results are different when you add the media with the Video Importer.
It also might be helpful if you opened the video you have in Media Info or G Spot and posted its audio and video specs for us.
That's what i'd like to know sucks doesn't it?
1st, Iphone won't easily edit http://forums.adobe.com/thread/881246
-and a fix http://forums.adobe.com/thread/934466
2nd, What are you editing, and does your project match your video?
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037
What is a CODEC... a Primer http://forums.adobe.com/thread/546811
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037
Report back with the codec details of your file, use the programs below... a screen shot works well to SHOW people what you are doing