Hi Tomasz,

The following code works on my side:

tvData.DoDragDrop(String.Format("=SayHello(""{0}"" )", item.Text),
DragDropEffects.Copy)

Where SayHello function is defined in VBA.

Drag & drop built-in functions also works:

tvData.DoDragDrop("=TODAY()", DragDropEffects.Copy)

Could you verify the actual string you're sending to drag & drop contains
the correct format of the formular?

Thanks,

Jie