I want to set up freeBSD to a 16 gb usb driver. I tried to plug my usb while installisation and got
Cam statues: CCN request completed with an error.
So how can I avoid these errors and setup FreeBSD to my usb driver?
Ehm, I don't understand what you mean by "usb driver". You mean umass(4)? That's just plug and play. It works or it doesn't, nothing to configure here.

Or do you mean to say you want to install FreeBSD on a USB stick or external HD? Again, the stick or external HD works or it doesn't. Memory sticks or external HD can be finicky though, especially the cheap ones.
Try another USB port (USB 2 port).