I was having a similar issue that I worked on for days (see 'big problem with the authentication required error') and I just fixed it by simply commenting out line 76 in osticket/login.php.
#@header("Location: view.php");
require('view.php'); //Just incase. of header already sent error.
exit;
Simply commented out the @[deleted] line and now client login finally works! Geesh, what a pain. Hopefully this'll help you.