To my surprise, I was not able to do so and I got following error.

The operation could not be completed. Invalid FORMATETC structure

Many of you may also get a similar error:

Invalid FORMATETC structure (Exception from HRESULT: 0×80040064 (DV_E_FORMATETC))

After few hours extensive searching on net and trying out many solutions, I got to know few things.

Microsoft uses this exception in many scenarios and not in a specific situation. This means the root causes can be different but it will show you only this error.

This makes you to try many solution. Unfortunately no solution listed on Internet worked for me and I was forced to find my own.

I’m listing my solution along with other solutions that may work.

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See Also:  MCTS 70-630 all you need to know to clear this exam

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I highly recommend to read all solutions and try the simpler ones first and then go for complex ones. This will save your day.

Solution 1:

ASP.NET 3.5

In my case I was using following hierarchy.

ASP.NET Button -> ThemedButton -> DesktopButton.

I didn’t wanted developers to start using ThemedButton so I don’t wanted to show it on toolbox.

So I put some attributes to it. Like below:

[DefaultProperty("Text"), ToolboxData("<{0}:ThemedButton runat=server>"), ToolboxItem(false), DesignTimeVisible(false)]

I don’t know the root cause, but removing following piece of code worked for me.

ToolboxItem(false)

Solution 2:

Resetting toolbox items has also helped many of them. (very simple solution)

Solution 3:

Remove all project reference and add them one by one. Recompile and done!

Solution 4:

Check if you are using old Ajax controls library. Make sure you use the latest one.

(Brian Chavez has posted a solution on this: Check here)

Solution 5:

Unloading a project that used Script#

(Brian Chavez has posted a solution on this: Check here)

Solution 6:

Unloading and re-loading the project. (very stupid, but works somehow)

Solution 7:

Adding new web.config file.

Just remove the old one and add a new one and then transfer your customizations (if any) to the new one from old one.

If you know more, then please comment.

This exception is thrown when you are trying to delete items of a collection in a for loop or using a for each loop.

The ideal solution could be to use a for loop with a descending counter.

Problem:

for e.g.

If suppose you are executing any of following code snippets

1.

for (int listcounter = 0; listcounter < ReferenceOwnersList.Items.Count; listcounter++)
{
ReferenceOwnersList.Items.Delete(0);
}

2.

foreach (SPListItem Li in ReferenceOwnersList.Items)
{
Li.Delete();
}

Here ReferenceOwnersList is a collection.

Now whenever this code will execute for the first time, the number of items reduce. So the second item gets the first index.
I tried deleting 0th item everytime but still I got the exception. Again changing index may cause skipping the items in most senerios.

And the collection throws the “Collection was modified; enumeration operation may not execute” exception.

Solution:

Solution
Use a reducing for loop.

for (int cntLi = ReferenceOwnersList.Items.Count – 1; cntLi >=0 ;cntLi — )
{
ReferenceOwnersList.Items.Delete(cntLi);
}

so that even if the last item is deleted, the index of other items wont change.