Anna-
Any off-the-shelf drive must be reformatted Mac OS Extended before attempting to capture with FCP.
Most come formatted for PCs. Even if it says it’s Mac formatted on the box, people usually find that the factory Mac formatting leaves something to be desired.
If there’s anything you’ve put on that drive you might want to save, put it somewhere else for safe keeping. Use Disk Utility to format the drive Mac OS Extended with journaling off. This will erase all information on the drive and leave you with a fresh drive that you can use for media.
Be ultra-careful that you are formatting the right drive. You wouldn’t want a mis-click to erase something else.
debe