Multicam Project Non-Stop Rendering

I created a multicam clip in FCP X.

I synched based on the first marker on each clip. I used a clapboard.

I using four clips and they're DV, so I know my system can handle it. (I've used five HDV streams with no problem.)

The rendering will not stop and it's been more than 20 hours since I loaded my last clip. I'm using a MacBook Pro conncected to an external drive via FireWire 800.

Another problem is that the audio and video are off by about a half-second. After dozens of multicam projects, this is a first for me.

Why is this happening? Could it be because I have FCP 7 and X on the same MacBook Pro?

I had a problem editing a multicam project on FCP 7 last week. The clips would not sync. When I moved my external hard drive to my Mac Pro, which does not have X, the problem disappeared.