osticket - admin login error "Authentication Required"

i have tried to setup osticket few times and i'm very sure that my admin username and password is correct but i still got error message "Authentication Required"

After browse and google around, i found one solution to enable me to login but i'm not sure what is the effact for this change.

go to scp/staff.inc.php, and find the line below

//1) is the user Logged in for real && is staff.
if(!is_object($thisuser) !$thisuser->getId() !$thisuser->isValid()){

comment out !$thisuser->isValid() and now become

if(!is_object($thisuser) !$thisuser->getId() /* !$thisuser->isValid()*/){

go to try again. it's working. Perhap, someone can tell me what is the issue and i'm not php expert. Not working on 15 Sep 2008

Update: 15 Sep 2008
No Luck. It only work for one day. Not sure what happen and now not working. I'll keep updating this post until get some solution or work around. I have to un comment previous changes.

Solution:
line 41 in scp\login.php, comment out @header("Location: $dest"); and try again.
// @header("Location: $dest");
it's work for me, at least for now.

Update: 21 Sep 2008
It's working fine since changes on 15 Sep 2008. SOLVED!