On November 11th, an Apple App Store bug surfaced , preventing apps purchased there from launching. This includes versions On The Job and Overflow purchased on the App Store. There are some steps that can be taken to attempt to repair the damaged apps. C-Command Software sums them up well on their site:
The problem seems to be that the certificate in the App Store's receipt expired. In some cases, when you try to launch the app you'll get a dialog from the App Store saying that the app was purchased on another Mac and asking you to enter your Apple ID password. Sometimes this will cause the system to download a new receipt, and everything will work. If entering your password doesn't help, we've heard some reports that it helps to restart the Mac and try again. Make sure that your Mac can connect to the Internet, or it won't be able to download the new certificate.
However, sometimes the OS will (for unknown reasons) still not be able to download a new receipt. In this case, it will report that the application is damaged and that you need to "download it again from the App Store." To do this, open the Applications folder, drag the app to the trash, and empty it. Then go to the Purchased tab in the App Store app and click Install to re-download the app.
If these steps do not resolve your problem, please download a version of On The Job directly from us. You will be able to use this version in trial mode while Apple addresses this problem. If needed we can provide a temporary license. If you need any further assistance please contact us.