FCP 6 rendering problem

[Lekid]

Hi guys, I'm hoping someone will understand my problem. I'm working on the latest MacPro with 8 gigs of RAM, so, memory is not a problem.

I have a project with few sequences of 1080 HDV i60 opened. One of them is running smoothly in the timeline and all the others are jerky and stop playing after a couple of frame giving me the message of the drop frames.

The only sequence that works lets me render it but the others don't. There's no rendering whatsoever to those jerky sequences and my question is... What is it? I usually had to render my timeline's clips but now it never asks me to do so and the clip is far from being smooth.

I hope someone can help me on this, I've been looking around for so long to find an answer.

Last thing, I've captured my video files on FCP5, so the files are located on my external hard drive and I've set the render files and scratch to my MacPro's HD... It was in my external before and I though I would give it a try.

Thx.