Tykes striker Craig Davies missed a spot kick three minutes before his namesake, Curtis Davies, headed home his second, and match-winning, goal.
Disappointed with his side, who have one win in 13 games, Hill blamed individual errors for the loss, including that of Davies' penalty miss.
He said: "We would have been 2-1 to the advantage but we've got to accept that he (Craig Davies) has made the wrong decision.
"He's scored penalties for us, important goals and today he's missed a penalty so I accept there are vulnerabilities to everybody.
"We have to take it don't we? It's a measure of the task that we've got. We look as though we're controlling a football match and maybe shoot ourselves in the foot - not once but twice, three times - the penalty as well, that's football.
"To be perfectly honest, the first goal I think it's a really good cross in. I think he's got between players and the goalkeeper.
"I think we've got to have a bit more assertiveness so I'm not going to lay blame, but the second goal, players have taken their own responsibility to change markers. Now it's not their responsibility to change who I allocate to mark at corners and set-plays and that's where we've been done."