You'll want to change the last name in the User table (not the aspnet_User table).  If the lastname field is NULL, it will break your user administration for that user.

Try inserting a lastname directly into the User table and see if that fixes both of your problems

Taken from forums some time ago. Don't remember the author and not tested yet

declare @oldName nvarchar(128)
declare @newName nvarchar(128)
declare @error_var int, @rowcount_var int
declare @newNameCount int

select @oldName = 'johndoe1'
select @newName = 'johndoe2'

begin transaction

 select @newNameCount = count(*)
  from Users
  where Username = @newName
 if @newNameCount > 0
 begin
  RAISERROR('Username already exists. @newName=%s', 10, 1, @newName)
  ROLLBACK TRANSACTION
  RETURN
 end

 update Users
 set Username = @newName
 where Username = @oldName
 
 SELECT @error_var = @@ERROR, @rowcount_var = @@ROWCOUNT
 IF @rowcount_var <> 1 OR @error_var <> 0
 BEGIN
  RAISERROR('Could not Update User.Username. @oldName=%s', 10, 1, @oldName)
  ROLLBACK TRANSACTION
  RETURN
 END
 
 
 update aspnet_Users
 set
  Username = @newName,
  LoweredUserName = LOWER(@newName)
 where LoweredUserName = LOWER(@oldName)
 
 SELECT @error_var = @@ERROR, @rowcount_var = @@ROWCOUNT
 IF @rowcount_var <> 1 OR @error_var <> 0
 BEGIN
  RAISERROR('Could not Update aspnet_Users.Username. @oldName=%s', 10, 1, @oldName)
  ROLLBACK TRANSACTION
  RETURN
 END

Commit transaction
go

---

Locopon
Free modules: E-commerce, Complete localization (Portal, page, module settings, skins, etc.), Secure Login, and more
http://dnn.tiendaboliviana.com