Berra was dismissed after 25 minutes for a tug on Troy Deeney that was adjudged to have denied a clear goalscoring opportunity by referee Graham Scott but Solbakken was unconvinced.
"I think I agree with everyone who say it's a very harsh one," he said.
"They thought a little bit about first coming to the ball and then the Watford player comes through one-against-one and he shoots and Carl (Ikeme) saves and everybody thinks it's over.
"There's no appeals from anyone, from a Watford player or even the dugout, and I think he (the referee) just created a problem for himself after that, but that's his decision.
"If you see the kind of tackles and things going on in the Championship, I think it is a very, very small body contact and I think it's a very harsh decision."
The dismissal caused tactical problems for Solbakken, who was forced to alter his formation accordingly.
"We wanted to come in at half-time only 1-0 behind and then we went through some different formations," he added.
"We started with 3-4-2 and then got a goal, went back and played 4-4-1 and 4-3-2 and I think we had to change a little bit to make sure we were higher up the pitch than we were in the first half.
"To be fair to the guys, they created some good chances in the second half."