Why does "Infragistics" folder generate a "missing assembly" compile time error?

Question

Dear community member.

While I have programmed in C# for a number of years, I must admit that I am new to WPF and Infragistics controls. Recently I came across an unexpected compile time error and I was wondering what might be causing it:

The type or namespace name 'Controls' does not exist in the namespace 'Sandbox.WpfApp' (are you missing an assembly reference?)

Thoughts?

STEPS TO REPRODUCE

1. Create a WPF project
2. Add a XamGrid to MainWindow.xaml
3. This step is important: name the XamGrid
   • <ig:XamGrid x:Name="abc">
4. Compile and run the application... everything is ok!
5. Create an Infragistics folder within the project
6. Add a WPF user control to the Infragistics folder
7. Compile the application: the before mentioned error is generated

What is interesting is:

• if you remove x:Name="abc" from the XamGrid => no compile-time error
• if at step #5 you had named the folder "IntragisticsTest" => no compile-time error

ADDITIONAL CONTEXT*

• Infragistics WPF4 controls (version: 12.2.20122.1000)
• Visual Studio 2013