Photoshop CS5 extended (extension manager not allowed me to connect with photobacks)

I have a CS5 extended which is registered under my name.  Recently, I bought a plug-in software "photobacks", I want to install it into my CS5 extended, but the extension manager said "You do not have the appropriate permissions required to perform this operation.  Contact your system administrator to obtain permission." I did chat with Adobe Customer Care so many times, but nobody can help.  Would any experts can help me to solve this problem.