power not transferred to transfer switch box

I have a 17500K Portable Generac Generator. During a recent outage in my area, I was unable to get the power to go through my transfer switch box (located on the outside by my electrical meter). It kept flashing green and red. Initially, I thought that something was wrong with the transfer switch box, but once power returned, the indicator on the transfer switch box was green. The system has worked in past outage. Any help would be greatly appreciated.