He told www.themillers.co.uk: "Its a loss on penalties but the game should have been put to bed by half time.
"We came out in the second half and just didn't start and the players are disappointed, I don't know if its a mental thing but we have given everything there's no doubt about that. Grimsby gave us a tough second half but we have to be able to cope with that and put teams to bed.
"In the first half our midfield did ok, and Peter Holmes showed no ill effects and was lively aswell as being unlucky with an effort on goal. Chris O'Grady came in to score a good goal with Marc Newsham buzzing and Jamie Yates had an outstanding first half - although he tired towards the end he has a big future.
"Generally it was a decent performance and we were just unfortunate in the penalties as it's a lottery. There was some tiredness and we're just trying to get a balance but that's difficult to do when you're playing six of your regulars but some lads have had invaluable experience.
"We'll do a warmdown and be ready to travel to Brentford on Friday."