WebClient.CancelAsync causes TargetInvocationException

[Cat]

I created an array of WebClients like this,
WebClient[] downloaders = new WebClient[10];

And started asynchronous downloading for each WebClients.
When the user wants to cancel the operation,
I did like this,
for(i=0; every downloaders...)
{
downloaders.CancelAsync();
}

This caused TargetInvocationException
Why? Do you know the reason? Please let me know.
Thank you.

 

[DBC User]

Did you make the async calls on the downloaders itself like
downloaders.BeginInvoke(...)???

 

[Cat]

No, I used
downloaders.DownloadAsyncData();

I used the cancellation code at the form's Closing event handler.
I found that using the same code other than Closing event,
it didn't causes any problem. Maybe there's something wrong
with the form's closing event and WebClient.

 

[DBC User]

If you can send me brief code, I can try to see if I can spot something
wrong.