We had this before on sync not reading usb sticks. Was something to do with the partition type not whether is exFAT or fat32.
Found it. Have a read here from thread #13
Does anyone have any clue how to get the maps update to actually install, I have tried it multiple times, followed the instructions to the letter exFAT formatted (not quick) unzipped the zip archive directly to the flash drive(s) (tried 3 so far) with 7zip & WinZip. and no matter how long I wait...
www.kugaownersclub.co.uk
I took andspenka's advice and didn't bother updating my sync2 from 3.08 but if you want to have music on your usb stick then you will need it to be able to read it.
I know the link I referred to is sync 3 but same issue could apply for sync 2 not reading some sticks. I have this on my works surface pro where it won't read my SanDisk ultra, yet plug it into my laptop and it reads it fine.