I have some code:

       Dim u As MembershipUser
       u = Membership.GetUser
       u.Email = Me.txtEmail.Text
       Membership.UpdateUser(u)

It's giving me this error:
ProviderException was unhandled by user code
The E-mail supplied is invalid

It's happening for the last line of code, UpdateUser.

u.Email is myaddress@mydomain.com, so it is valid.

Sometimes this happens, sometimes it doesn't.

Any ideas why?