WP e-Commerce Multisite Problem

I will be brief, my problem is that since i enabled multisite function in my site, a php error appears in the top of my site.

This is the message:

Warning: strpos() [function.strpos]: Empty needle in /home/w*****n/public_html/wp-content/plugins/wp-e-commerce/wpsc-core/wpsc-functions.php on line 695

and the line 695 says:
if( ( $wp_query->is_404 && !empty($wp_query->query_vars['paged']) ) || (isset( $wp_query->query['pagename']) && strpos( $wp_query->query['pagename'] , $wpsc_page_titles['products'] ) !== false ) && !isset($wp_query->post)){

What can i do now?