Wordpress-chat-plugin Installation Error

Hello,

I am using XAMPP for windows for offline install and using wordpress version 3.0.3 ... now when i install this plugin wordpress-chat-plugin .... i get an error while activation ....

Fatal error: Call to undefined function is_site_admin() in C:\xampplite\htdocs\wp1\wp-content\plugins\Wordpress-Chat-Plugin\update-notifications.php on line 418

Now I have tried to solve it but I can't find any solution .... now this error is given by all the plugins ... so can you tell me where i am getting wrong and also i have followed the installation guide given on website .. but still getting the same error .......

Hope there will be some reason that i am not able to find out ...

so any one can help me in solving this error ............

Thanks
Fluidswork