When grouping multiple sites in the same app pool we have the following warning logged in the event viewer and the sites become unavailable.

Exception type: NullReferenceException

Exception message: Object reference not set to an instance of an object.
at Tridion.ContentDelivery.AmbientData.HttpModule.OnRequestStart(Object sender, EventArgs e)
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Edit: Tridion Version 2011 SP1 H1
Windows Server 2008 R2
.Net v4

Has anyone seen this before or have any advice I can try?

Any advice would be great.

  • Afaik multiple websites in the same app-pool should be no problem (for the Ambient Data Framework). Can you double check if the individual sites are configured correctly (Ambient data config in web.config)? Do they work if you run them isolated in their own app-pool? Which version of Tridion/Windows/IIS/.NET? Commented Jun 16, 2014 at 18:40
  • Hi Albert, yes they work fine when they are in their own app pools, and I've updated the post with the environment information. thanks
    – Martin
    Commented Jun 17, 2014 at 9:41
  • We heard from SDL support that this is not a supported configuration. Commented Sep 10, 2014 at 9:57

2 Answers 2


A bit of a trivial piece of advice, I'll offer it anyway: use a separate Application Pool for each web site.

My guess is that the .NET wrapper, Juggernet, spins up a JVM for each app pool, and this does not play nice when multiple sites try to use the same Java heap space.

  • Hi thanks for the info. Do you have any advice then for if you have a global rollout of sites, how sites could be grouped for performance reasons?
    – Martin
    Commented Jun 17, 2014 at 9:44
  • 1
    @Martin, I don't really understand what you mean here. Are you trying to economize on memory? Setting up a separate App Pool per site should give you better performance from the point of view of having more granular control. If one pool of one site goes bad (for whatever reason), it won't affect the other sites. Commented Jun 17, 2014 at 12:52

I will suggest to put the logs in debug/trace mode, and check at what step its breaking. because error provided by you is generic not giving any clue. In logs you should see...

"Ambient Framework initialization"

and other messages.

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