Can't Access Network Admin

I uploaded this plugin WP-CopyProtect [Protect your blog posts]
I installed it and then in the next screen I clicked on “Network Activate” and got this message:

Fatal error: Call to undefined function wp_get_current_user() in /home/frezpz/public_html/3sides/wp-includes/capabilities.php on line 1281

I then clicked on my sites admin (dashboard tab) and it worked fine and even the plugin I just loaded and installed was working fine.

But when I tried going back into the Network Admin area I got the same error message as above.

Anyone have any fixes or suggestions.

Thanks in advance