I have tried this too, freshly installed yesterday, added a couple of tickets, some are assigned, some aren't.
It should be 1.6.RC5 as that is what I downloaded.
Now I'm seeing the same errors as above #1054 - Unknown column 'staff.firstname' in 'field list'
or when I remove the staff.firstname and leave only the staff.lastname: #1054 - Unknown column 'staff.lastname' in 'field list'
Both in de errorlog in the admin panel as in phpMyAdmin when I paste the code in the SQL query window.
I went over my code several times (this is the only modding I've done on my installation) and I don't see anything wrong.
Any suggestions, please? I'm not experienced in writing php, nor SQL queries, so most of it is Chinese to me. I try to understand, but I don't get why it doesn't "see" the staff.firstname, while I do see those in my database. And they are not empty either.