Adam, thanks for the prompt reply, I managed to get my wrapper working earlier today, this is the first chance I have had to leave feedback:

• The reason I received the error was because I had used ConfigurationPath to set the configuration. It seems that if an item such as "LinkTree" is missing from this ConfigurationPath file then any attempt to cast it to CuteEditor.TreeDropDownList results in an "Invalid Cast Exception." In this situation setting TemplateItemList seems to result in malformed controls when the control is missing from the ConfigurationPath file.
  
  
• In your example which is also in the dev manual you use the following line:
  
  dropdown.Items.Add("<span style='font-size:18pt'>5 </span>(18pt)", "5 (18pt)", "5")
  
  The HTML in the above line is rendered as text and not HTML so the span tag is of no real use here.
  
  
• The manual also references the button control "Links" numerous times ... I believe this should be "LinkTree"
  

I hope this is useful to you.