Pray Love Remember, Pray Love Remember - S1-E14
Continuity mistake: Danno walks several feet into McGarrett's office to make a report. Though there's no break in the dialogue and no time for him to have moved, the shot cuts and he's suddenly standing outside the door as they finish their conversation. (00:02:45)
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.