Problem with Final Cut Pro - General Error

Hi, I'm new here and I've been dying to ask for someone's help on this. Since none of my friends are video editors or Mac users, it was difficult to find some. And I Googled/Binged my problems but nothing helpful came about.

So I'm a video editor. I came from a Windows computer so I was used to using Sony Vegas and Premiere Pro. Now I am more comfortable with Sony Vegas because it was simpler but Premiere Pro was/is good too. I heard Final Cut Pro is very similar to Vegas so naturally I decided to go with this product.

It's great BUT there is a slight problem. Every time I try to import a file that isn't .MOV but is Quicktime/iTunes compatible, I get a "General Error" message. This happens with .MP4 files. Does this happen to anyone eles or does anyone know any fixes/codecs I can install? Any help would be appreciated.