Are you using target manager and debugger? If so, you have to go to target manager everytime you attach a process and click kernal explorer and the "green" play button for it to unfreeze. Or you might have installed mw3 patches wrong or have a bad eboot.bin. Make sure you install mw3 patches from 1.19 in order up... 1.19, 1.20, 1.21, 1.23.