Standard Operating Procedure in the professional world is to create at least 1 backup of the camera files (I usually create at least 2). This backup is considerably smaller than the files after log and transfer. You can then delete your ingested media after the job is complete and restore your project if necessary in the futre. And being an old f*rt, even with copying the files before ingesting them into fcp, it's still way, way faster than capturing in real time which is what you had to do in almost every case with a tape based workflow. And as Nick said, disk space is really, really cheap.
That said, if you want to spend the time troubleshooting this problem, I'm happy to help. And it's never a bad idea to figure out what's going on in these cases as it may be symptomatic of a larger problem.
Repair permissions. Applications: Utilities: Disk Utility
Try creating a new account in system preferences: accounts. Log out and log in with the new account and see if that makes a difference.
Do you have at least 10% free space on all drives and are all drives formatted macosextended?
Are you running any other programs at the same time? Do you have any other peripherals connected at the same time besides the camera?