WSAT Security tab error for Custom Role provider

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ASP.NET

I have created a custom Membership Role and Profile provider using INGRES db. Now I can see my IngresMembership and IngresRole provider in the Provider tab (Select a different provider for each feature (advanced) ) of WSAT but when I clik on security tab, I get this error:

"There is a problem with your selected data store. This can be caused by an invalid server name or credentials, or by insufficient permission. It can also be caused by the role manager feature not being enabled. Click the button below to be redirected to a page where you can choose a new data store.
The following message may help in diagnosing the problem: Object reference not set to an instance of an object."

What am I missing? Do I need to add code for all override methods for Role provider? I have just written code for the Initialize and GetRolesForUser functions.

Thanks!