<<the internal drive 2, but it's full...>>
It had better not be "full" in any sense, with less than 10% space free. FCP needs ALL the connected drives to be running cool and relaxed, as in not close to maxed out. Especially the system drive, which is busy with virtual memory and its own scratch space while FCP is doing the very intensive task of capturing video.
Shane's advice about always setting a Capture Now limit is key. The first thing FCP does during Capture Now is pre-allocate all the disk space it will need to capture what the limit is set at, whether you're going to capture that much or not. If you set no limit, it tries to allocate the entire disk. If it's a big, empty one, that's going to take a long time (spinning beach ball) and it's easy to think the process will never end. And you'll probably find, after that force quit, that there is a humongous file on the scratch drive that is fully useless. That's your big allocation, and you need to dump it before starting over.
There are so many good reasons to use Log & Capture vs. Capture Now....
Scott