Try a different USB port and see if that helps. Also try using a different USB cable - some custom cables disable the power connection which may prevent the devices from handshaking correctly.
If that doesn't work...
The X-1 shouldn't need a USB driver but the older variants apparently did.
http://www.peachtreeaudio.com/support/usb-drivers.html
I don't suppose the MacBook Pro had drivers installed previously, did it?