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I am trying to add an assembly to configuration/system.web/compilation/assemblies - but with the following code it I get Expression must evaluate to a node-set.

private SPWebConfigModification CreateWebModificationObject()
        string strUniqueName = string.Format("add [@assembly='{0}']", typeof(HowsYourDayHub).AssemblyQualifiedName);
        string strNode = "configuration/system.web/compilation/assemblies";

        SPWebConfigModification webConfigModification = new SPWebConfigModification(strUniqueName, strNode)
                Owner = "HowsYourDay",
                Sequence = 1,
                Type = SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode,
                Value = string.Format("<add assembly='{0}' />", typeof(HowsYourDayHub).AssemblyQualifiedName)

        return webConfigModification;
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Okay I found a solution with a console app - seems like a previous modification was stuck:

            SPWebApplication webapp = site.WebApplication;


after clearing every modification it started working!

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