Sharing Application In Collaboration is not working

Hi

I am doing share application in CLP.... when i am clicking on the "Share Application" i getting the following error...

You cannot start an application sharing session since all the invited users are already in another application sharing session or have not yet replied to another pending invitation.

This is first time i am doing share application collaboration.....

why i am getting this error... how to resolve it....

please help me..

Thanks & Regards

Ravi Shankar B