What method did you use to create the persistence?  Did you use Unetbootin to create persistence, or did you put one of the pre-configured persistence files onto your USB drive?  I'm not sure if Unetbootin's method of creating persistence works. 

Check out the wiki if you haven't.  It explains a method to create persistence that has worked for me multiple times.

http://www.linuxcoin.co.uk/wiki/index.php/Persistence