An Allegiant McDonnel Douglas MD-83, registration N415NV performing flight G4-682 from Orlando Sanford,FL to Grand Rapids,MI (USA) with 142 passengers and 6 crew, was climbing through about FL270 out of Orlando Sanford, when the crew stopped the climb due to problems with the cabin pressure. Descending normally the aircraft returned to Orlando Sanford for a safe landing about 50 minutes after departure. The flight was cancelled, the passengers were rebooked onto flight G4-5682 the following day and reached Grand Rapids with a delay of 21 hours. The airline reported the cabin pressure did increase during the climb, the captain decided to return to Orlando out of abundance of caution, returned the cabin pressure to normal levels. The passengers not living in the Orlando area were taken to hotels, all passengers were given 150 US$ vouchers for future flights.