Nath's Blog

Life. Through the eyes of Nathan Coad.

Citrix Web Interface and OWA

So today I thought I’d do something a bit radical.  I already had a working Outlook Web App installation, and a working Citrix Web Interface installation.  However, they were on different servers, and I have only one IP address.  What to do?

It occurred to me I should install the Citrix Web Interface on the OWA server.  Genius!  But it turned out to not be quite so straightforward.  Because I’m running Exchange 2010, the OWA server was running Windows 2008 R2.  Citrix have only recently released Web Interface 5.3, which supports 2008 R2.

I decided to give it a go.  Firstly I needed to install J# 2.0 Release 2.  Installation of the web interface went smoothly, using the default web site.  OWA and Citrix live in separate folders, which means they would co-exist reasonably well.  Or so I thought.

After creating a citrix web interface site, I attempted to load the page, only to be met with “HTTP Error 503. The service is unavailable”.  After some investigation, log reading, head scratching, and google searching, I discovered the answer to my problem.

The pertinent error message was “The Module DLL ‘C:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll’ could not be loaded due to a configuration problem”.  The answer turned out to involve editing an IIS configuration file, “C:\Windows\System32\inetsrv\config\applicationHost.config”.

The line

<add name=”kerbauth” image=”C:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll” />

needed to be changed to

<add name=”kerbauth” image=”C:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll” preCondition=”bitness64″ />

I thought that would be enough to resolve the problem, but it wasn’t.  Turns out I had to make the same changes to the lines referring to owaauth.dll and airfilter.dll

Once I’d made those changes, and restarted IIS, everything was fine.  I was greeted with the familiar Carbon-themed interface, and a working web interface installation.  Hooray!


  1. Hi Nathan, I have exactly the same problem in the same configuration but adding preCondition=”bitness64″ doesn’t change anything, the kerbauth.dll error in application log is still here (so is the http error when i try to browse on the citrix web interface). How did you get to this conclusion ? Thanks

  2. I solved my problem with delete/recreate exchange kerbauth module and owaauth/airfilter isapi filters

  3. encode

    November 25, 2010 at 8:14 pm

    Great to hear that NiTRo. Sorry I didn’t reply to your comment, but it’s been such a long time since I had the problem that all I can remember is what I’d already written down.

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