Couple of problems with the Tb1 My Passport Essential SE

I’ve been transferring AVI files from my old harddrive to my new and only some will play.  I dont understand why? Also with my old Harddrive I used to play my movies (AVI Files) through a Media Player Adaptor so i can watch my movies on TV, with no problems. Now having transfered most of my movies from my old Hard drive to my new one (My Passport Essential SE) and plug it into the same Media Player Adaptor and loads of films are missing?? Please can some Help?

Are the 2 drives formatted the exact same way?

As Pizza mentions if has to be the file system, verify your drive format.

make sure that when you copy files that you always safely remove the drive when you are done.  cause it could cause corruption if you just pull the plug, which is what the symptoms seem to point to.  Also, is the media device not reading any of the files or just not all of them?  can you see and play the files from the drive on your computer?