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Individual Tax Module | How to resolve the HTTP Error 503 Service Unavailable error when opening ITR12

Published:  18/05/2017
How to resolve the HTTP Error 503 Service Unavailable error when opening ITR12

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  1. When navigating to IIS and find that the CQS ITM application service has stopped under Application Pools
  2. Start the CQS ITM service, navigate to Default Web Site | TaxWareITR12 and ITR12 
  3. Right click navigate to Manage Application | Browse and you receive HTTP Error 503 Service Unavailable error message
  4. Upon navigating back to Application Pool you discovered that the CQS ITM and DefaultApplicationPool services had stopped again.
  5. When opening the Windows Event Logs and find multiple errors for IIS-W3SVC-WP 
  6. Details of the error pointed to kerbauth.dll failing to load 
  7. The file is located on an Exchange Server (e.g. C:\Exchange Server\Bin\)


What is the cause of this error?

The application pool was stopped because of by default 5 consecutive exceptions within 5 minutes which is default behavior for IIS worker process.

This issue starts happening if during re-install of the Exchange Server, you select a different location to install.

When Exchange server was installed for the first time, it registers its custom modules with IIS and for this it makes entries in the IIS root config file
i.e. applicationHost.config at this location C:\Windows\System32\inetsrv\config. These enties are made under the <globalmodules> section.
  • You will see one such entry for kerbauth.dll.
  <add name="kerbauth" image="C:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll" />

While uninstalling the Exchange from the server, these entries might not be removed from the applicationHost.config.
Issue starts when while re-installing the Exchange, the installation drive is changed. So such dlls will be copied at some other location while this entry is not modified in the applicationHost.config file.
While accessing the website, IIS will try to load this dll from the old path C:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll while this dll is not there and exists at some other path now.

How do I resolve this error?

To resolve this issue, you need to manually change the path of kerbauth.dll to the latest path where exchange has been installed during reinstall.
  • Open ApplicationHost.config file at this path C:\Windows\System32\inetsrv\config using notepad
  • Find the entry for kerbauth.dll for example similar to the following:​
<add name="kerbauth" image="E:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll" />
  • Change the path for this dll as per the latest location of the Exchange Server installation files.
​<add name="kerbauth" image="C:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll" />
  • Save the changes and stop and start the IIS services.
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