As rambo47 suggested the application is corrupted or the data reference is. An Index error pointing to index 18 usually indicated a record that was expected was missing. this can be due to you deleting a contact or something and when you performed a backup you copied the problem and simply replaced the problem when doing a restore.
In any event good luck. The link below will offer some of the other errors FB can see.
KB25378-Facebook 2000 series error codes in Facebook for BlackBerry smartphones