Error on installing WPMU Plugin on Local Host

I am trying to create a test environment for wordpress. But when I try to install the WPMU Dashboard plugin, it show the following error.

" This local development site url has previously been registered with WPMU DEV by the user Adam(a** To use this site url, connect with the original user or upgrade your trial to a full membership. Alternatively, try a more uniquely named development site url. Contact support if you need further assistance.?

Please help.