Silverlight - KeyNotFound Exception

Finally, I found out the reason for this exception in Silverlight. Though I had put try catch blocks in all the methods, sometimes this exception is thrown.
I had a doubt that it may be because of animation. And, it was.

I was using storyboard1 for opening canvas1 and storyboard2 for closing it.
And canvas1 opens when i do a mouse enter event to another canvas-canvas2. Similarly, canvas1 is closed in the mouseleave event of canvas2.
The exception was thrown only when I did a fast mouse enter and mouse leave(ie before storyboard1 ended and storyboard2 was called).
So, it is always better to stop all the storyboards modifying the control before beginning a storyboard for animating the control.