It means someone who is confused. It;s orogns date back to an early dice game. The original game was called To Set On Cinque And Sice which were thought the riskiest numbers to throw for, and anyone who tried was probably confused. over time, the numbers have sifted to six and seven, and one theory is that those numbers add up to thirteen, which has always been considered unlucky. Through time, the phrase has settled into "all at sixes and sevens" meaning to be confused or muddled.
Andy's dice-game explanation is certainly by far the most likely, but if you click http://www.randomhouse.com/wotd/index.pperl?date=2 0000331
a link will take you to a website which offers two other possible sources, including a biblical one.
I still opt for the tradesmans guilds story.......heck i like it and i don't care....BTW this isn't a complaint but when you posted the question didn't it come up with matches for this as being already asked??? or is the search engine being duff as usual?