please ignore - I was missing the dll that unzipped the file when it was dropped

Is there anything special that I need to install to allow a drag and drop operation to take place?

I have a C#, XAML, .NET 4.0 application which handles the dragging of a file from Windows Explorer and dropping it on my application window fine. However, when I run this at my client's site on a Windows XP computer the pplication runs fine, but the drag code that I have in my grid_drop event never fires.