I've noticed that a lot of people here have been having this problem. To fix this, SSH into your phone and do the following:
navigate to
/private/var/mobile/Library/Customize2/Cache
delete all of the files that say
ThemeListByChar0 thru
ThemeListByCharZ
Now when you go back into Customize2 and browse themes, it'll re-check the online directory for themes rather than checking the cached file.
Don't forget to hit "thanks"