FCP3 scratch space problem

[rick gordon]

Here I was trying to kick off a "Capture Now" from a long tape, and FCP 
keeps saying:
"Insufficient Disk Space remaining in the capture scratch'

Except that I have 64GB of disk space currently selected - a couple of 
18GB partitions on an external FW drive and the remainder on internal 
drives.
What's worse is that I'm trying to capture audio only. So I have plenty 
of disk space.
What in the world is it looking for/at?

Very frustrating... any clues?