Have you recently removed any battery cables just before this started happening? As said above you should check that you don't have a swapped positive and negative wire.
Also two things I would try,
Buy an electrical outlet tester at your local home improvement store. Spend the extra dollar for the tester that has a GFCI test button. Test all the outlets in the RV and see what the tester says.
Most generators have an open neutral by design. This can be fixed by purchasing a replacement plug at you local home improvement store. Then ground the neutral and ground by placing a short jumper between neutral and ground screws in the plug. Insert the plug into the generator and the open neutral should go away.
