I did some reading on your problem and it seems like another possible solution would be to try formatting the drive to FAT and not FAT32. Another possibility is the drive has failed. After a certain number of read/writes the flash memory starts to go bad. How long have you had it and how often do you use it? Since you don't have an optical drive we need to determine if your USB drive is the problem or if it's your computer that's causing the issue.
Alternatively you can say **** it and run BT4 out of a VM.