Rekordbox crashing when USB is plugged in

I recently lost everything on my laptop and I'm trying to get everything back in place. i use to run rekordbox 3.2 and it worked fine but not i have just synced all of my iTunes playlists on to rekordbox 4.0 it is really messing up. I have a brand new USB formatted on FAT32 that has never been used. At first i synced all of my music onto it and inserted it into my xdj1000's and it was bugging out and skipping through the songs which i thought was a bit weird. But then when i plugged the usb back into my laptop to add some songs it came up with the message ' contents are corrupt' 'delete, yes or not' So i deleted and then cleared the usb, reformatted it and tried a few more times and it just did the same thing. Whenever i plugged the usb in again it corrupted the files. Now for some reason i can't even plug my usb in when it has files on it without Rekordbox completely crashing with the 'Application error' Message. Need to fix this as soon as possible as i have a big event coming up and i run all my editing through RB