Scotland defender Berra was handed his marching orders for pulling back Troy Deeney, despite the fact that the striker carried on and managed to get a shot at goal.
"I agree with everyone who says it was a very harsh one," said Solbakken. "I think the referee just created a problem for himself, but that's his decision.
"Berra didn't take away Deeney's big chance. There was very small body contact."
The defeat to the Hornets saw Wolves drop to 16th in the Championship table.