Developing Project and configure Database

Hey....
I have created one project using sitefinity project manager.
After creating it i right-clicked that created project and click on browse.
then in the browser it will ask me to set the database.
i have given the database server name and intial database name.
then  after it ask me to register administrator so i given inforamtion of first name,last name username ,password and email.
 and i clicked on continue.
and it give me error that

The specified role "Administrators" already exists.

please give me the solution to reslove this problem.
what could be the possible steps so that i can make it correct.
Thanks.