thanx to Quinnx!!! i was getting this problem too worked for hours on a song .. then got memory full error when i tried to save although project was on the usb drive, etc etc i did this:
When you get MEMORY FULL when trying to save to USB,
Open Device manager/Sound video game controlers
right click on FantomG and choose Disable (or just unplug the usb cable)
Try save to USB once more and it should work with no error.
And it worked thanks!