There are reports for upgrades of sites using Artisteer Templates:
Fatal error: Cannot access protected property ContentViewArticle::$user in /home/xyz/public_html/templates/bpmusic_v1/functions.php on line 561
And others report this: Fatal error: Call to a member function getMessageQueue() on a non-object in /home1/xyz/public_html/templates/otd_white/functions.php on line 165
It is also reported that Artisteer plans to release a Joomla 1.7 compatibility release in the next few days.
According to Artisteer Tech Support Artisteer 2.6 is not compatible with Joomla 1.7. Artisteer Tech Support suggests using Artisteer 3.0
This is the reason for the error: "Fatal error: Call to a member function getMessageQueue() on a non-object in /templates/ functions.php on line 165"