It could well be your database was damaged during the update (or prior). If you haven't opened / closed rekordbox more than once, you may be able to recover them if it's just a new thing...
Open the following location:
Win 7/8: C:\Users\yourusername\AppData\Roaming\Pioneer\rekordbox
OSX: /Users/yourusername/Library/Pioneer/rekordbox
Rename datafile.edb to datafile.edb.old
Rename datafile.backup.edb to datafile.edb (removing .backup)
See if that helps.