Export crashes Fcp and Finder and empties Start-Up Disk

I am editing a 10-min Apple ProRes ,1920x1080, 23.98fps sequence (footage from 7D normal speed and slowmo conformed with Cinema tools). I work on an external Lacie 2BIG.

Everything works fine in editing and rendering. The problem is in export. When it finishes exporting the sequence, it crashes fcp, I am even unable to successfully force quit it, and it also crashes the Finder. I reboot the computer leaving the HD on. When I try to open the exported sequence. mov file, it crashes Finder. On top of all that, I cannot eject the HD from the computer. In the background, in the Activity Monitor, I see that my startup disk from 17gbs, within half an hour it reaches to 0kb and an empty start-up disk message appears. Only then, I can eject the disk. When I restart the computer, without the disk, the start-up disk memory is back to normal.

The result is I cannot successfully export the sequence.I tried the process with a different HD and the same happens. The problem seems to be only with that project.

Please let me know what is going wrong, in five years time, it's the first time I encounter this issue.

MacBookPro with 2.2Intel Core Duo, 2GB Ram, MacOSX 10.5.8, Final Cut Pro 6.0.5

Thank you all, in advance!