[wp-hackers] Plugin or theme hack help needed...

[MarvinC]

This cross-post may be titled wrong but I'm hoping I can get some help with
a theme who's plugin doesn't work under WPMU. When activated the following
error appears:

Fatal error: Call to undefined function wp_get_current_user() in
/home/content/k/g/m/haiti/html/wp-includes/capabilities.php on line 969

I've tried replacing the capabilities.php file but it didn't work and I've
also tried de-activating the plugin and customizing the template using just
the stylesheet. So as a last straw, and abvious show of desperation, I've
posted this error on the author's blog, the WP & wpmu forums, and now here.

Any responses appreciated.