Title gives the brief of my question.

We are trying to have an environment for our web application
application in sharepoint 2010.

1.)an LDAP provider (for intranet users authentication)and
2.)a SQL provider(for internet users authentication)
3.)same URL to be used.

My understanding::

we can configure forms based authentication using an LDAP provider or with a SQL provider.

Challange::

We want to have both LDAP provider and SQL provider to use in forms based authentication.

What i tried:

1)created web application (Defalut Zone)
2)configured with LDAP
3)Extended the web application to Intranet Zone configured with SQL Provider

Problem:

4.)When updating the Web.Config of CentralAdmin (which already has LDAP provider) with SQL Provider.
Central Admin is not working. Throwing some Error:500 Internal error.

Queries::

1.)how to configure both providers in web.config of Central Admin and SecurityToken

2.)Are there any other ways to do this


Thanks in Advance...