Not that you asked, but here is a long explanation for a short expression, from Michael Quinion, writing on international English from a British viewpoint:
The expression 'sixes and sevens' is commoner in the UK and Commonwealth countries than in the US. It can mean something that’s in a state of total confusion or disarray, or people who are collectively in a muddle or at loggerheads about how to deal with some situation. For example, a British newspaper article in 2002 reported that the Conservative opposition had accused the Government of being “at sixes and sevens” over what to do with the rail network.
But what could possibly be the sixes and the sevens that are involved? There are two old stories that try to explain this. One tries to find it in the King James Version of the Bible; Job 5:19 has “He shall deliver thee in six troubles; yea, in seven shall no evil touch thee”, a couplet that makes no sense to us today and which doesn’t seem to link to any known use of the expression. The other story, more common and very widely believed, traces it back to a dispute between two of the ancient livery companies in the City of London.
These companies, trade guilds, grew up from the latter part of the twelfth century as associations to protect their members’ interests. (They were called livery companies because members had the right to wear a distinctive costume or livery.) There was a lot of squabbling with other guilds about precedence in the early days. One especially troublesome dispute concerned the Merchant Taylors Company, whose members were tailors, and the Skinners Company, whose members controlled the trade in furs. In 1484 the then Lord Mayor, Sir Robert Billesden, settled the dispute in a judgement of Solomon by ruling that the two companies should alternate between the sixth and seventh positions in successive years, a ruling still in force. This might seem to settle the matter. What could be clearer? The two companies were permanently at sixes and sevens with each other.
The problem lies in the brute force of the evidence. The first form of the phrase wasset on six and seven. Geoffrey Chaucer uses it like this (“to set the world on six and seven”) in his Troilus and Criseyde, dated about 1375. There are several other examples in the following century, which show that Chaucer was making use of an expression already well known (to the extent that he didn’t feel the need to explain it). The appearance in Chaucer was rather more than a century before the dispute between the guilds was settled, so can’t have been created as a result of it (though I can imagine people using the saying to make a joke about the dispute after it had been settled).
We can’t be absolutely sure of where the phrase comes from, but the most probable explanation is that it arose out of an old game of dice called hazard, in which one’s chances of winning were controlled by a set of rather arbitrary and complicated rules. It is thought that the expression was originally to set on cinque and sice (from the French numerals for five and six). These were apparently the most risky numbers to shoot for (“to set on”) and anyone who tried for them was considered careless or confused. Later, the number words shifted to their modern values as a result of folk etymology among individuals who knew no French and misheard the words. The link with the game (and the original French words) must by then have been severed, or perhaps it was a joke, as seven is an impossible number to throw with one die. The change may also be linked to the sum of the new numbers being thirteen, long considered unlucky.
The phrase has been common since Chaucer’s day, to the extent that we can trace in detail the way its form has shifted down the centuries, including set at six and seven,stand on six and seven, and to be left at six and seven. Shakespeare used it in this last form in Richard II, in which the Duke of York says: “I should to Plashy too, But time will not permit. All is uneven, And everything is left at six and seven”. It took until the eighteenth century for people to commonly put the numbers in the plural; for example, Captain Francis Grose included it in his Dictionary of the Vulgar Tongue in 1785 as “Left at sixes and sevens, in confusion, commonly said of a room where the furniture, etc. is scattered about, or of a business left unsettled”.