EW end up too high.

W/NS
♠	A 10 7 6 3			♠	K 8 5
♥	K 6 5			♥	Q J 8 4
♦	K Q 7 2			♦	J 9 3
♣	3			♣	Q 10 2

4♠ is defeated by one trick.
'I preferred playing 3♠ rather than defending, that's why I bid 3♠', says West.
'I though you invited for game', says East, 'and I have a maximum hand, so...'

Who erred?

Solution

Every partnership should discuss situations like these. It is logical that West bids 3♠ with the intention of playing there, but how is East to know he is not supposed to bid game with a maximum hand?
A good agreement in such a situation: 3♠ is to play and therefore not a game try. Three in another suit is the game try for 4♠. In case there is no bidding space in another suit (in the bidding above: if NS bid hearts, not clubs) the invitational bid is double! (This is called the 'maximal double' in the US and you have to mark your convention card if you play it.)
On the assumption EW have agreed on this, East's 4♠ bid is therefore wrong.

A few examples:

¹ Not invitational to 4♠ (this was the actual bidding problem); West is merely contesting the part score 

¹ Trial bid: invitational to 4♠
 

¹ Penalty double 

¹ Not invitational to 4♠; West is merely contesting the part score 

¹ Invitational to 4♠ (West cannot double 3♥ for penalties!)