When a program stops responding or crashes, Windows asks you if you would like to send an error report to Microsoft, to help them see what programs crash with what errors and also which programs are unstable with their OS. You can turn it off by going into your Control Panel and double clicking System. Click the Advanced tab and then click Error Reporting (at the bottom of the window) Then click the disable error reporting option. Critical errors will still cause a pop-up, just not the error reporting window.