Continuity mistake: McGarrett has infiltrated a crime syndicate and is standing on the patio of a beachside house with two men and a woman while Danno, in a boat several hundred yards offshore, is taking pictures with a camera and telephoto lens. When the pictures are developed, the background in the photos is the ocean, not the beach house and patio.
Character mistake: To get on board a private yacht, Carl Swanson poses as a repairman from Mauna Loa Refrigeration Company but the name on the back of his uniform is misspelled "Muana Loa."
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.