[Plugin: Easy Nivo Slider] Fatal error when I try to access Network Panel(On Multi-SIte installation

Hello !

I have just installed the plugin on a Multi-Site Installation. I didn’t activate it Network wide. But just on main Site. Immediately I lost access to /wp-admin/network/ and got this error message :

Fatal error: Call to undefined function wp_get_current_user() in /public_html/wp-includes/capabilities.php on line 1028

I have double checked it by de-activating the plugin, deleting and re-installing it. But got the same error all the times

It only happens when the plugin is activated and works fine if I de-activate it

Does any body have Idea on solving this issue?

Versions used :

WP Version : 3.1.1
Plugin Version : 1.6.1
Multi-Site Installation ? Yes

Thanks !