Setting Up An Alternate Login To Sa

In times past I connected my web app to SQL Server by embedding the following in the web.config file:
    <connectionStrings>
      <add name="XyzApp_DB" connectionString="Data Source=MyServerSQLExpress;Database=XyzApp;User ID=sa;Password=secret_password"/>
    </connectionStrings>
 
And it worked fine.  But it was pointed out to me that this wasn't a very proper way to do things.  So I was advised to set things up with a different connection string:
    <connectionStrings>

      <add name="XyzApp_DB" connectionString="Data
Source=MyServerSQLExpress;Database=XyzApp;User
ID=Xyz_Admin;Password=different_password"/>

    </connectionStrings>
 


To get this to work, I've followed these instructions:

 
A
more secure login than “sa� is required to access your application.
  In the “connectionStringsâ€? section of
“Web.config� you’ll find a User ID called “Xyz_Admin�.
  Here are the steps to ensure that your
DB has this login id:


a.       Using
the Microsoft SQL Server Management tool, look in the root for the “Security�
folder and open it.
  Inside that, open
the “Logins� folder.


b.      If
“Xyz_Admin� doesn’t exist then right-click on “Logins� and choose “New Login�:


                                                  
i.           
Enter “Xyz_Admin� in the “Login name� textbox.


                                                
ii.           
Click on “User Mapping� on the left side and in the
‘Map’ column check the box beside “XyzApp�.


                                               
iii.           
Go back to the “General� page and choose SQL Server
Authentication.


                                              
iv.           
Specify any secret password you wish.


                                                
v.           
You can uncheck “Enforce password expiration� if you
wish.


                                              
vi.           
Specify “XyzApp� as the default database and press
OK.


c.      
Open “Databases�, right-click on “XyzApp� and
select “New Query�.
  Run this query: sp_change_users_login 'update_one',
'xyz_admin', 'xyz_admin'






 
Now, I was pretty sure that this procedure was working fine but it doesn't seem to work for me today.  I know that the client computer I'm using can connect to the DB on the server because I temporarily changed the User Id to "sa" and it connected fine.  But when I change it back to "Xyz_Admin" it does not.  So I'm thinking that there's something incorrect with the procedure above but I don't know what.
Any ideas?
Robert W.