I have had that problem on occasion and as THE MEEKER said it was corroded terminals on the plug.. I now carry a can of Brake Clean for when this happens .. spay it into the male plug let it drip out and try plugging in ... works for me every time...
2004 Chev Silverado Duramax optioned past the max. 2009 Jayco Eagle 308 RLS 765 watts of solar, 6-6 volt batteries (696 amp hour), 2000 watt (4000 surge) whole house inverter.
140 days boondocking in 2016
211/2015, 196/14, 247/13, 193/12