Solution for "The underlying provider failed on Open" exception.

As you guys know that I am posting enterprise architecture design article in code project here. While preparing third part, I started to implement simple tier application for demo. After completing server side implementation, I started to implement simple client for demo purpose. Once completed with client, i tried to run my demo application. But unfortunately I got the strange exception called "The underlying provider failed on Open". I googled more than an hour and found that most of the folks facing the same issue when they try to call the service which contains database access in local sql server through IIS. But no one is providing proper solution for this issue. Everyone says that IIS uses network credentials when it contacts sql server authentication process. So we should grant access to "NT AUTHORITY\NETWORK SERVICE" to your database.
But this is not the right solution and no one is saying how to fix the issue. After spending some hours, found the solution and my app running without any issues.
 

Here is the solution.
 

As folks mentioned IIS user network service user credentials while trying to log in sql server. So just change the Application pool settings in your IIS.
 
Step 1:
Open Internet Information Service Manager
Step 2:
Click on Application Pools in left navigation tree.
Step 3:
Select your version Pool. In my case, I am using ASP .Net v4.0. If you dont have this version, select DefaultAppPool.
Step 4:
Right click on step 3, and select advanced settings.
Step 5:
Select Identity in properties window and click the button to change the value.
Step 6:
Select Local System in Built-in accounts combo box and click ok.
That's it. Now run your application. Everything works well.
 
Enjoy!!!.