Do you know what the CODEC inside the FLV is? MediaInfo should be able to provide that information.
IIRC, as of abut CS 4 (maybe with one of the updates), PrPro has had native support for FLV's with the On2 VP6 CODEC. I do not believe that Sorenson Spark is supported.
I can't believe I actually managed to "fool" Premiere CS6.
First, I tried to import a full HD flv which is about 1.6 GB. Then I read this thread, installed the On2 VP6, opened again Premiere, tried to import again the flv video, but still "Unsupported or damaged file" message.
Then I had this brilliant idea that had also helped me in a similar situation:
So here are the steps explained in a very easy and detailed description:
1. Go to any folder, or "My computer"...
2. If you are on Win 7 /Vista hit "ALT" on the keyboard and the "File, Edit, Tools.." toolbar will appear in the upper side of the window
3. Click on "Tools" > "Folder Options" > "View"
4. Under the "Advanced settings", there is a long list of options. Look for "Hide extention for known file types" and deselect it.
5. Hit Apply and OK.
Your video file should be now like: "videoname.flv"
6. Right click on the file, select "Rename" and simply change the extension from ".flv" to ".avi", let's say.
That's what I did and I tried importing again the video with the new extention to Premiere CS6.
Oh, and afer that you might go back to the folder options and select again "Hide extention for known file types" if yout dont want to see the extentions for all your files.
Nice try, doesn't work anymore on CC 2017 eheh!
You need to convert them outside of PRE first (ideally to DV or HDV). You could try the free Handbrake transcoder.