Azman with Forms based authentication in asp.net 2.0

Hi,
I have been trying to use the Authorization Manager with forms authentication. I have followed the instructions at http://msdn2.microsoft.com/en-us/library/ms998336.aspx but still get an error when I try to add a user to a role.
If I run:
Roles.AddUserToRole(usr.UserName, "TRole");
I get the following exception: "No mapping between account names and security IDs was done. (Exception from HRESULT: 0x80070534)"
I am able to retrieve the roles in azman using say Roles.GetAllRoles(), but I cant figure out how to add a user to a role using the Roles and Membership Framework.
Below is what the relevant sections of my web.config looks like:
<connectionStrings>
    <add name="LocalPolicyStore"
         connectionString="msxml://C:\RolesData\KaizenStore.xml" />
.....</connectionStrings>
 <authentication mo ...