Can't Update Email Id - MembershipUser

 In my site I am trying allow the users to update their Email Id.
When user trys to update his email id it gives an error saying -


The E-mail supplied is invalid.



I am using the following code-

MembershipUser user;

user = Membership.GetUser(HttpContext.Current.User.Identity.Name);

user.Email=txtEmail.Text;

Membership.UpdateUser(user);

This error comes only when there is another user who uses the SAME EMAIL ID.
I am using email id as the user name at the time of registration, BUT I DON'T UPDATE
the login email Id (Username) in this code as you can see it clearly.
Any idea!
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