Windows 2003 /DC : Application Server Unavailable

While we were hosting an web application on IIS ,got this error
Application Server Unavailable
The web application you are attempting to access on this web server is currently unavailable.Please hit the "Refresh" button in your web browser to retry your request.

On inspecting further the event log has captured following
aspnet_wp.exe could not be launched because the username and/or password supplied in the processModel section of the config file are invalid.aspnet_wp.exe could not be started.HRESULT for the failure: 80004005

Explaination:
By default, ASP.NET runs its worker process (Aspnet_wp.exe) with a weak account (the local machine account, which is named ASPNET) to provide a more secure environment. On a domain controller or on a backup domain controller, all user accounts are domain accounts and are not local machine accounts. Therefore, Aspnet_wp.exe fails to start because it cannot find a local account named "localmachinename\ASPNET". To provide a valid user account on the domain controller, you must specify an explicit account in the section of the Machine.config file, or you must use the SYSTEM account.

To work around this problem, use one of the following methods:

• Create a weak account that has the correct permissions, and then configure the section of the Machine.config file to use that account.
  
• Set the userName attribute to SYSTEM in the section of the Machine.config file.
  
• Configure the section of the Machine.config file to use an administrator account.
  

One other special value for userName is System, with the password AutoGenerate, which runs the process as an administrative account and allows all ASP.NET user code running under the process to have full administrative privileges.
For deployment on local development environment one can use 2nd option , for deployment on client side 1st option is the best.