Creating boot disk for Windows 7 on MacBook Pro
Try using dd instead of asr.


Use mount to determine the device path of your attached USB disk.  Find the disk itself and ignore the individual partition numbers.  EG: if you get /dev/sda1 just use /dev/sda for the next steps.
Unmount the disk in the Finder.  
Construct and run your dd command as such: dd if=/path/to/windows7.iso of=/path/to/usb/device