Multisite Content Copier Error

Hi. I have made several attempts to copy a small number of posts from my site http://voices.dyc.edu/students/ (site id 2) to my site http://voices.dyc.edu/demo/ (site id 6) using the Multisite Content Copier plugin. Each time, nothing was copied. However, twice when going to the destination site to check whether the content had copied, I received this error message:

Fatal error: Call to undefined function wp_generate_attachment_metadata() in /home/blogweb/public_html/wp-content/plugins/multisite-content-copier/inc/content-copier/content-copier-post-type.php on line 548

When I refresh the browser page, I see the admin interface as usual.

Please let me know why the Multisite Content Copier is not working.

Thank you,
April

P.S. The other WPMU plugins I have installed and in use are:
Domain Mapping
Cloner
Google Maps