Town were beaten 44-22 by Featherstone Rovers last week, and Veivers felt his team made too many mistakes.
“I thought we had an opportunity in the first half to go with them but we just came up with too many errors,” he said.
“I was disappointed with how we played in the first half but we held together in the second half, we played some good footy and defended okay.
“It was a game of two halves in a sense but again it’s about concentration levels.
“Defence is a big issue for us. We haven’t got issues with scoring points, that’s been there all year for us but defensively we have to be a lot stronger than we are.
“Dewsbury post a threat in the halves and they’ve got some speed out wide to cause some problems.”
“I thought London were pretty good, their defence was outstanding,” he said.
“They didn’t give us a chance to play and unfortunately some of our boys didn’t turn up and give their best. So we probably got the result we deserved.
“It’s always difficult to travel up there [to Workington], they’re in desperate need themselves so it’s a big game for both teams to get some points on the board.
“If we want to finish where we want to be at the end of the year this is a must win game.”
Scott Hale is missing for Rams with an ankle injury.