All a region checkpoint does is compare an image to another image with a pixel tolerance. Usually, there is a base image that is stored and then compared to the "live" image in the application.
Is it possible that, when running the automation, that there is a delay in the application that the automation is running too fast for? For example, say the radio button is unselected. You run a test step to select the radio button and then do the region comparison. However, the application hasn't rendered the radio button as selected yet when the region checkpoint kicks in and so the comparison fails.
OR.... it might be one step sooner than that... say, for example, you have some sort of step that needs to execute in order to enable the radio button for selection. That step executes but there is a short delay in enabling the button. TestComplete assumes the radio button has been selected but it, in fact, hasn't been. And then, the region checkpoint fails.
In short... it doesn't sound like a problem with the region checkpoint but in timing in your automation... the fact that you can manually run it at "human speed" up to the check point and then fire the checkpoint seems to point in this direction... Try "slowing down" the automation run by injecting delays to see if that solves your problem. If it does, I'd replace the injected delays with smarter code to wait for something to happen before going on to the next step. WaitAliasChild or WaitChild methods or WaitProperty methods or something like that will allow you to build in these delays to allow the application to catch up before the automation attempts an action.
