How to restrict Active Directory Users to bind into the Drop Down List in Manage Users Permissions

Hi All,

We have created manage users permission page where we can manage user permission using Sp service.

But we are getting duplicate users in the Drop down List. we under stand that users are binding Active Directory user+FBA Users.

But we want to restrict Active directory users to bind into Grid View.

We did managed Users permission page below url Reference.

http://sympmarc.com/2011/11/03/managing-sharepoint-site-user-memberships-in-multiple-groups-using-spservices/

Can any one suggest me..How to restrict those Duplicate Users.

Thanks in Advance.