It sounds like double pane windows incorporate a hermetic seal that some how in your case has been compromized. If you can remove the entraped mositure you would need to re-seal the pane to avoid problems in the future. Airplanes have triple pane windows with the tiny holes. They fog and then clear up. The reason for the holes however is to limit pressure drops between the apnes. I would consider you issue as a matter of keeping the dew point within the gap between panes below the gap temperature. This depends on the environment on both sides of the pane. If the offending pane is near a dishwahser ot shower, then it might be more difficult to solve.