I got that error after trying to drag in an ASP.NET AJAX Toolkit control.  After I rebuilt my entire solution that I was working with, I could then drag it in just fine.

In my case, it happened when my page contains errors (which i knew) that i tried to drag a control from the toolbox. Same error appeared as discuss here.

So what i did is remove all occurences of errors, and then build the solution. Once successful, i tried dragging the controls again, it worked!

I just got a report of the same thing from a customer using EasyListBox in VS 2008 (though I know there are others with 2008 and they've had no trouble).  ELB has public a public constructor in each class, and again, some folks are using it in this environment with no trouble at all.  No ToolboxItem attribute either.

Anyone from MS want to comment? 

 I ended up just reinstalling VS I believe.  Or porting over the code to a brand new web project.  I can't remember which but one of them resolved this.

Hi, Dil!

I had the same problem with the custom control I developed. All of them had the ToolboxItem attribute set to true. When I removed it, all controls works fine. Very nice!

Thanks!!! 

Dil:

I found it..!! 

I have used this attribute in my custom control and it throws the same error.,,!!   When I removed its working fine.!! 

[ToolboxItem(true)] 

 

Thanks

Dil

Odd enough, as i thought the problem was with my custom control's assembly being referenced in the wrong way, simply adding the "public" declaration over my custom control class did do the trick for me. I've been encountering this error when dropping my custom control in source-view.

Thanks alot :)

I found that there are many situations where you might get this error.

There are around 7 solutions. But I couldn't post all of them here.

I have tried to list most of them here.

Solution: Invalid FORMATETC structure

P.S. One of my blog reader also found a solution.

 check here

http://codeforfuture.com/2009/02/04/solution-invalid-formatetc-structure/

 Not sure if above link is working properly so reposting.