Eddie Howe insisted hard work on the training ground was in order after the Clarets crashed out of the Capital One Cup at Swindon.
Charlie Austin's 10th goal of the season - making him the country's top goalscorer - was not enough after first half goals from Paul Benson and Andy Williams gave the Robins a two-goal lead at the break thanks to defensive errors.
A third goal near the end from Troy Archibald-Henville sealed a miserable night for the Clarets.
And Howe pulled no punches after admitting his side were struggling to cope with opposition set plays.
He said: "It was disappointing because don't get me wrong, we wanted to win tonight. It was a big opportunity to get into the last 16.
"With two wins in three you think we have turned the corner and we then seem to fall back again and it's a big challenge for us, because I don't think the ability in the squad is in doubt, but we have to deliver it.
"We had a number of chances tonight and played really well for the first 20 minutes.Charlie had a couple of chances and they've had one off the line, but they scored and goals change games and we have rocked a little bit.
"We conceded a poor second and from there it was pretty forgettable really.
"The second phases from set plays are consistently causing us problems and I really don't know where that has come from because we dealt with set plays really well last year.
"We do feel we will always score goals but we do have to tighten up. That is our big objective now.
"It's hard work on the training pitch to put it right. There is no other way and if we take away those second phase set plays we defend ok.
"But that just shows how much work we have to do in that area."
The Clarets made five changes, with Brian Jensen, Michael Duff, Joe Mills, Marvin Bartley and Brian Stock all starting.
Howe explained: "Jason Shackell and Junior Stanislas were both injured, Cameron Stewart was cup-tied and Martin Paterson was rested for obvious reasons.
"I feel we missed those players and it's given us food for thought.
"But if we can get a win now against Millwall on Saturday, the world will look a better place."