is_network_admin()

Hi,

I installed a new wordpress on my site http://kindleromania.ro/store.
Then I added the framework theme and activated the Marketpress plugin.

Now I get the following error:
Fatal error: Call to undefined function is_network_admin() in /home/kindlero/public_html/store/wp-content/plugins/marketpress/marketpress.php on line 375

How can I resolve this error?

Thanks,
Daniel