Inventor 2026 WPF APP error/bug/exception

[basautomationservices]

Hi all,

When running my add-in with inventor 2026, I get an error when I save a document. 

My addin is a dockable WPF window where you can edit iProperties. 

I have a feeling it could be related to a mismatch in package versions. Error is thrown from inventor DLL's.

Exception info below:

System.Windows.Markup.XamlParseException
  HResult=0x80131501
  Message=Add value to collection of type 'Microsoft.Xaml.Behaviors.TriggerActionCollection' threw an exception.
  Source=PresentationFramework
  StackTrace:
   at System.Windows.Markup.XamlReader.RewrapException(Exception e, IXamlLineInfo lineInfo, Uri baseUri) in System.Windows.Markup\XamlReader.cs:line 401
   at System.Windows.Markup.XamlReader.RewrapException(Exception e, Uri baseUri) in System.Windows.Markup\XamlReader.cs:line 396
   at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlReader templateReader, XamlObjectWriter currentWriter) in System.Windows\FrameworkTemplate.cs:line 780
   at System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(DependencyObject container, IComponentConnector componentConnector, IStyleConnector styleConnector, List`1 affectedChildren, UncommonField`1 templatedNonFeChildrenField) in System.Windows\FrameworkTemplate.cs:line 687
   at System.Windows.FrameworkTemplate.LoadContent(DependencyObject container, List`1 affectedChildren) in System.Windows\FrameworkTemplate.cs:line 517
   at System.Windows.StyleHelper.ApplyTemplateContent(UncommonField`1 dataField, DependencyObject container, FrameworkElementFactory templateRoot, Int32 lastChildIndex, HybridDictionary childIndexFromChildID, FrameworkTemplate frameworkTemplate) in System.Windows\StyleHelper.cs:line 920
   at System.Windows.FrameworkTemplate.ApplyTemplateContent(UncommonField`1 templateDataField, FrameworkElement container) in System.Windows\FrameworkTemplate.cs:line 494
   at System.Windows.FrameworkElement.ApplyTemplate() in System.Windows\FrameworkElement.cs:line 1706
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3485
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV) in System.Windows.Controls\Grid.cs:line 1454
   at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged) in System.Windows.Controls\Grid.cs:line 1393
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint) in System.Windows.Controls\Grid.cs:line 986
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3538
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint) in System.Windows.Controls\Grid.cs:line 1051
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3538
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV) in System.Windows.Controls\Grid.cs:line 1454
   at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged) in System.Windows.Controls\Grid.cs:line 1393
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint) in System.Windows.Controls\Grid.cs:line 1006
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3538
   at System.Windows.UIElement.Measure(Size availableSize)
   at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint) in MS.Internal\Helper.cs:line 320
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3538
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Documents.AdornerDecorator.MeasureOverride(Size constraint) in System.Windows.Documents\AdornerDecorator.cs:line 72
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3538
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint) in System.Windows.Controls\Grid.cs:line 1051
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3538
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Border.MeasureOverride(Size constraint) in System.Windows.Controls\Border.cs:line 368
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3538
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Window.MeasureOverrideHelper(Size constraint) in System.Windows\Window.cs:line 2328
   at System.Windows.Window.MeasureOverride(Size availableSize) in System.Windows\Window.cs:line 1743
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize) in System.Windows\FrameworkElement.cs:line 3488
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Interop.HwndSource.SetLayoutSize()
   at System.Windows.Interop.HwndSource.set_RootVisualInternal(Visual value)
   at System.Windows.Window.SetRootVisualAndUpdateSTC() in System.Windows\Window.cs:line 2209
   at System.Windows.Window.SetupInitialState(Double requestedTop, Double requestedLeft, Double requestedWidth, Double requestedHeight) in System.Windows\Window.cs:line 2194
   at System.Windows.Window.CreateSourceWindow(Boolean duringShow) in System.Windows\Window.cs:line 2053
   at System.Windows.Window.ShowHelper(Object booleanBox) in System.Windows\Window.cs:line 3427
   at System.Windows.Window.Show() in System.Windows\Window.cs:line 1450
   at System.Windows.Window.ShowDialog() in System.Windows\Window.cs:line 1549
   at Autodesk.Inventor.Dialogs.FileDialog.FileDialogTerm.StartFileDialogModal(String messageName, BinaryReader inputs, BinaryWriter replies)
   at Autodesk.Inventor.IPC.InputMessageChannel.SendMessage(Byte[] message)
   at WHxMessageChannelNative.SendMessage(WHxMessageChannelNative* , RMxBinaryBuffer* inputs, RMxBinaryBuffer* outputs)

  This exception was originally thrown at this call stack:
    [External Code]

Inner Exception 1:
ArgumentException: Cannot add instance of type 'EventCommandExecuter' to a collection of type 'TriggerActionCollection'. Only items of type 'T' are allowed.

[JelteDeJong]

Hi Bas, I am not familiar with this exception. Why do you think it has anything to do with your WPF forms? I would investigate the Inventor save events. I noticed some new behaviour (in Inventor 2025 coming from 2023.) For example; it reacts differently when you abort an transaction in an event function.

But if you expect problems related to a mismatch in package versions, you could check if all your Microsoft/system packages have version 8.*.* I noticed that the 9.*.* versions are not always working correctly. Not sure if you are using DevExpress, but you could also check that version.

[basautomationservices]

Hi Jelte,

Thanks for the reply. Me neither..

I had a feeling the WPF forms were causing it cause of a previous error, this happened when I tried to use a datePicker from MahApps.Metro and it conflicted also in the Microsoft.Xaml.Behaviors library. 

I thought so cause when I debug that add-in and save a document it throws this exception. I came from 2025 to 2026.

Will investigate further 🙂

[basautomationservices]

Investigated a bit further.

I found that if I remove the reference to Xaml.Behaviors completely from my project, I don't get the exception anymore. Don't know if it's just because i'm not loading that debug information anymore.

I added the Xaml.Behaviors DLL from the inventor directory as a reference, and the error is gone. The version on that DLL is 1.1.39.xxxx, the version i get from Nuget is 1.1.39. Don't know what exactly is the problem but for me it is fixed now.

[jjstr8]

Are you (or a library you're using) using a reference to System.Windows.Interactivity from Blend?