Thank you for writing to us. I am glad to hear that you managed to resolve the experienced issue.
Generally, all you need to do is to add a reference to the Telerik.WinControls.UI.Design dll and reopen the file you want to edit.
Alternatively, you can install the Telerik.WinControls.UI.Design.dll in your GAC (our installation does this automatically) which will allow Visual Studio to resolve the design-time implementation without any additional references.
I hope this helps.
All the best,
the Telerik team
Q3’10 SP1 of RadControls for WinForms is available for download
; also available is the Q1'11 Roadmap
for Telerik Windows Forms controls.