When browsing to a site hosted in IIS 6.0 you may receive a “Service Unavailable” error. The cause for this issue can be an application pool identity that is not a member of the IIS worker process security group.

Issue:
The typical cause for a “Service Unavailable” error when browsing to a site in IIS 6.0 is that the Application Pool is running under an identity that is not a member of the IIS worker process Active Directory security group. Complete the steps in the following section to resolve the issue.

Resolution:
To resolve the issue follow the steps listed below:

Note: Steps 7 – 11 require access to a Domain Controller as well as Domain Admin privileges.
 1.  Open IIS Manager (Start | All Programs | Administrative Tools | Internet Information Services (IIS) Manager)
  2.  Expand the Web Sites folder and locate the application folder that the problem site runs under.
  3.  Right click the application folder and select properties
  4.  Note the name of the application pool that is listed on the Virtual Directory Tab and click OK.
    

 
    
 
  5.  Under “Application Pools” in IIS locate and right click on the application pool listed in step 4 and select properties.
  6.  On the Identity Tab note the name of the user that the application pool is running as and click OK.
Note: If the application pool is running as a predefined user such as “Network Service” then the following steps will not resolve the issue. Please see section 6 for links to other troubleshooting documentation.

 

  7.  Open Active Directory Users and Computers
  8.  Locate and right click on the IIS_WPG group and select Properties.
  9.  On the Members tab, click Add and type the name of the user from step 6.
  10.  Click OK to add the application pool user to the IIS_WPG group.


 
  11.  Restart IIS
  12.  Open Internet Explorer and connect to the site that was giving the “Service Unavailable” error.

If you continue to receive the error after completing the preceding steps follow the See Also link listed for additional troubleshooting steps.