well first off you shouldnt be using mp4s to edit with. Its a delivery format rather than an editing one. However it should still load I think. Did you copy it from a removable device? Maybe it is locked and you dont have permissions to use it. Single click the file and prss apple-I to get the info window up to see if your user has write permissions.
Mp4s are the only files i have to edit with. I only have copies of the final projects on a dvd and i have to rip them from that to upload them and edit them together. Is there a way to change the format? What format should I be using? When I get the copies of the films should I ask for a particular format that they can give me? And if so, what is that? i use handbrake to rip the dvd. Maybe i can change the format there?
I opened the infomation window (thank you for that info by the way) and it says my user has read & write permissions and its not locked or anything. Any other thoughts?