Correct a Botched Joomla Upgrade

This project is urgent. Please only bid if you really know what you are doing. I am a university professor. I have a Joomla site which I have spent days working on. I was using a component called "Ninja Site Styler"- one of its functions is to upgrade your Joomla install to the latest version. I clicked on this button today (to upgrade my site from Joomla 1.5.9 to Joomla 1.6. There was an error in installation, which has rendered my site inaccessible. When I go to my homepage I now get the error Fatal error: Call to a member function get() on a non-object in /sitename/libraries/joomla/user/[login to view URL] on line 214 The Ninja Site Styler forum is useless, and my web hosts have not responded yet. I need to get this site back asap. If you can get it working, you get paid. Simple as that. I don't care whether you have to downgrade to Joomla 1.5.9. At this stage I'm really not concerned about the upgrade. I just want my site working again. Thanks for your interest.