Continuity mistake: Aboard the boat, when Danno draws his gun, both his suit and his tie change colors and patterns completely between takes.
Here Today, Gone Tonight - S5-E17
Continuity mistake: Danno boards the helicopter without his briefcase, but arrives to conduct the interview carrying the case and tape recorder. He takes the copter back home again with nothing in hand, getting into his car empty handed as well. But he enters McGarrett's office carrying the briefcase again.
Continuity mistake: McGarrett wears a blue suit on the ride to the airport, but when he gets out of the car, his suit is brown.
Death is a Company Policy - S5-E1
Continuity mistake: The Five-O computer here lists McGarrett's name as Steven J. McGarrett. But in "A Gun for McGarrett," his middle name is revealed to be Aloysius. Strange that the computer doesn't know the name of its own department's head.
Continuity mistake: After murdering the cop, Frank and Luther steal a rifle from the squad car, then close the door. No one goes near the car again, but a few minutes later, the door has re-opened itself. (00:06:00 - 00:11:15)
'V' For Vashon: The Father (2) - S5-E10
Continuity mistake: From his office on the second floor, McGarrett looks out at the office building across the plaza. But the POV shot that follows is taken from ground level.
Continuity mistake: When the police cruiser with Danno aboard leaves HPD HQ, it's a 1967 Ford Galaxy 500 with wind wings. But in the next shot of it on the Honolulu streets, the car is a '71 or '72 model with no wind wings. (00:43:30)
Answer: He was fired. He never really appreciated his character. He felt Kono was portrayed as a big dumb Hawaiian and that the stereotype was racist. He also felt underutilized. He was fired after a heated argument with the show's publicist regarding his character. It seems there's not much details given regarding the incident or the firing, so it's seems possible he upset the show's producers as well.
Bishop73
No he said something derogatory about one of the Jewish producers that's why he was fired.