The Clock Struck Twelve - S5-E12
Plot hole: As a security test, McGarrett secretly has several dummy bombs planted in the court building, then later shows the governor where they are. Each time he pulls one of the devices from its hiding place, citizens in the courthouse stroll casually by without so much as glancing at the loudly-ticking "bomb." No one knew about the test, so McGarrett's bombs should be attracting some attention, if not causing outright panic. (00:05:00)
The Clock Struck Twelve - S5-E12
Character mistake: After distracting the guards, Danno tosses a grappling hook onto a ledge and climbs the side of the building. He then goes about his business, carelessly leaving the hook and rope dangling from the ledge for all to see. For a seasoned 5-0 team member, that's pretty sloppy covert operations. (00:22:40)
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.