Thanks for the detailed instructions on how to set this breakpoint!

I am using the Infragistics mmUltraTextEditor so I looked into mmUltraTextEditor.cs from the Infragistics Controls project as well as what you have suggested.
I did not find a StateChangeHandler() method in mmTextBox.cs (or mmUltraTextEditor.cs)

In the region ImmBinding Members, I found public virtual void OnBindData method.
I placed my breakpoint in this method's mmBindingStrategySimple.BindData(this, bindingSource, e); code line.

This breakpoint was never reached while running the code either with the Dim WithEvents CSForm As New CompanySelectionForm code line commented or uncommented.

It seems that none of the breakpoints I am setting in mmUltraTextEditor.cs are being reached while running the code.

Any further thoughts?