Invalid FORMATETC structure Error
Problem:
Usually, you get this error when an assembly reference in your Visual Studio is messed up.
In my Visual Studio 2008, I was getting this error when drag and drop a control from Toolbox to a XAML page.
"The operation could not be completed. Invalid FORMATETC structure."
Resolutuon:
I right click on Toolbox and selected "Reset Toolbox" menu item. It resets the assembly and control references and I no longer get this error.
More Solutions:

Wild LarPosted Sep 17, 2009, 3:13 PM
Mahesh Rules!
Jayvardhan PatileditedPosted Feb 11, 2009, 3:05 AMEdited Apr 9, 2009, 5:49 AM
I found that there are many situations where you might get this error. I have tried to list solutions for most of them. Solution: Invalid FORMATETC structure Jayvardhan Patil http://codeforfuture.com