Can you possible provide more information?
Like which version of the program are you using and on what operating system?
What model of camcorder is your video coming from and what is the video's resolution and file format?
What are you doing when you see this message?
Premiere elements 14 and using Windows 8. Initially I was downloading video from my gopro 4. My videos were viewable from premiere elements 14. I was even able to share on my facebook pages. For some reason out of the blue I am now unable to open my videos in premiere elements it states the issues above. When I try to open the project in premiere elements it tells me the file is not supported or the required codec is missing. I am unaware of anything I did differently to my project. I can see the black pages with the titles and hear the music but not see the videos now at all, I see something written in Chinese it looks like. you can tell where all video boxes are and everything looks as though it is ok per the previous setup except videos will not open in premiere elements. I can view them in windows media player with no issues but not through premiere elements. I also used to be able to open the projects from the drop down boxes, now it has a page that pops up and makes me select the project from the download box but says file is not supported or the required codec is missing. Hope this was more helpful.
Do you have Quicktime 7 installed, per the program's system requirements?
I do have quicktime 7 installed. I did make a mistake though, I have windows 10 not 8.
Trash all the media cache in the Prefernces.
Go to that folder and delete the rest manually
Rename the top folder the gopro footage is in
and try again.
Best is to transfer gopro footage first to harddrive then import into Elements.