Lee Miller put the visitors in front but the home side drew level when Luke Freeman was tripped in the box by Troy Archibald-Henville and Greg Tansey stepped up to slot home from the spot.
But two late goals from Matty Robson and David Amoo put the game to bed.
"It was not good enough all the way through the team," said Hartley.
"We seem to be going backwards at the moment. We had an honest chat in the dressing room and there are a lot of things we need to put right.
"If we're going to do something this season we need to accept criticism and turn it into something positive as all teams go through periods like this.
"It's a long season and you have your ups and downs but I don't know why it went wrong. Everything has been great all week and I can't put my finger on what's happened.
"It's a long process as we've got a lot of new players and the fans have to stick with us as there is a lot of willing in the dressing room."