The error message, "The given key was not present in the dictionary" is returned when adding a new ArcGIS Pro ProWindow item in a sub-folder of an ArcGIS Pro Add-In C# Project in Visual Studio 2019.

Workaround

For the workaround, there are two options:

• Add the ProWindow item directly in the Project main folder, or
• Use the workflow described in the Steps to Reproduce, ignore the error, then manually add the DAML code associated with the ProWindow item into the config.daml.

Adding the ProWindow item directly in the Project folder

Create a new C# ArcGIS Pro Add-in project, then add a ProWindow item, for example, right-click ProAddModule7 > Add > New Item > ArcGIS Pro ProWindow.

This correctly adds the ProWindow Item DAML code and other files (e.g button images) as shown in the figure below.

Executing the project produces the correct results as shown in the figure below.

Steps to Reproduce