ActiveDirectoryMembershipProvider not initialized

[Guest]

I am trying to write a change password routine using the new
ActiveDirectoryMembershipProvider. My code is below. I'm getting an exception
saying that my ActiveDirectoryMembershipProvider has not been initialized.
Can you guys point me to something that tells me what I'm doing wrong, please?

bool checkItOut;
string ls_retVal = "";
ActiveDirectoryMembershipProvider obj = new
ActiveDirectoryMembershipProvider();
try
{
checkItOut = obj.ChangePassword(as_userName, as_oldPassword,
as_newPassword);
}
catch (Exception ex)
{
ls_retVal = ex.Message;
}