I am using this app to scan ZXING barcodes:
https://github.com/jmawebtech/BarcodeReader-MonoTouch
If I enter the application, scan a barcode, press the home button, re-enter the app, and click scan, I see a black screen that looks like a camera shutter never opens. I have attached an image to this ticket.
If I press cancel, and go back to scan I see the camera open again.
How come the camera never opens on some occasions?

I had to add this code to Info.plist:
UIApplicationExitsOnSuspend YES
To App Delegate, I had to add this code:
The video recorder, which was used in this software, cannot run on a background thread.