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Do you have the latest version of QuickTime installed?
Also try to rename the .MTS file to .M2TS and then try to import the file.
Try to copy the media file to some other location like desktop and then try to import the file.
Please mention the name and model no. of the camera that you are using.
What computer operating system is your Premiere Element 9 running on? And, are you running the 9.0.1 version of Premiere Elements 9?
What are the properties of your source media?
Interlaced or Progressive
Pixel Aspect Ratio
There are video/audio readout programs that we can go to for that information if you do not know. But a quick way, may be to give the brand/model/and settings for the camera that recorded that AVCHD video.
The usual questions:
1. Do you have the latest version of QuickTime installed on your computer with Premiere Elements 9.0/9.0.1?
2. Are you running the program Run As Administrator and from User Account with Administrative Privileges?
The only AVCHD that I am aware of that cannot be imported into Premiere Elements (any version) is AVCHD.avi. Lots more questions and answers. So your reply with more details will help us to help you.
Looking forward to your follow up.