not able to add login module to authentication stacks!

HI Portal Gurus!

we are implementing siteminder sso integration with portal.

Iam trying to do following configuration ...

Modify the ticket authentication template:

a.)Remove from the stack:

1)BasicPasswordLoginModule

2)EvaluateTicketLoginModule

b.)Add the following modules to the top of the stack, in the order shown:

SiteMinderLoginModule

CreateTicketLoginModule

Iam not able to do either reomove exting one nor add new login module.Iam getting an error"Unable to add login module to authentication stacks! "

Ilogged in to v.admin as administrator with admin & superadmin roles.

It would be great if anyone could help me in this .

Regards

tag