The problem stemmed from a throw in awarded to Stoke, Lambert believes that the throw should have been theirs but the referees assistant thought different.
Shotton took the throw, it was nodded on by Jerome and Etherington who went past Ward with ease before beating the keeper from a tight angle.
Lambert said: "I think it was our throw.
. "He (Oliver) is walking away as if he has given it to us, and he actually raises his hand a little bit as if it is a Norwich throw, and then the linesman has overruled him for some reason.
"Our lads think it is our throw, we are out of possession and then we lose a bad goal. I think it was there for everybody to see that it was a Norwich throw.
"He (Oliver) did admit it to me in the tunnel that he was going to give it to us, but the linesman has overruled him.
"It is frustrating. We never had many chances in the game and never really got going with any fluency.
"This is a really hard place to come - you have to combat that aerial threat, which I thought the lads had done really well. But the throw-in changed the game."