Gary Johnson was a picture of frustration after he watched Yeovil throw away points with defensive errors in a 3-2 defeat at Carlisle.
Twice Yeovil hit back after Carlisle had taken the lead only to concede an injury-time goal to the Cumbrians' Ivorian striker Francois Zoko.
Johnson said: "It was defensive indecision for all three goals. Certainly a case of poor defending. We'll have to take a good look at it. We had chances and two goals should have been enough to win it.
"We got back to 2-2 deservedly in the second half and were slow going for it, but a moment's indecision for the third goal meant we lost the game we should have got something out of."
Johnson added: "Individuals have got to work hard on their decision making and defending because at the moment that is what is costing the club. All players make mistakes, but it's how many they make that is the important thing and if it keeps happening then you have got to change the personnel."
Jonathan Obika cancelled out Lee Miller's first-half penalty early in the second half and Dominic Blizzard equalised for a second time after Paddy Madden struck a second for Carlisle, but Zoko bundled home the winner in the third minute of time added on.