First I want to let you know that we do not support using ImgX in .NET. You might consider using our DotImage product instead.
You say this happens on a child form; have you tried doing the same in the main form? If it works on the main form then you may have to change your application to run the scan from the main form.
Make sure if you call OpenTwain that you always call CloseTwain on the ImgXTwain object before the form is closed.
One other thing you might try is to force the ImgXCtrl to be disposed or set to null in the form's Closing event.
Glenn Chittenden Jr.
Atalasoft Development Team