After many months of planning we discovered that there was a fundamental flaw with our new system. So, it’s back to square one (wieder am Nullpunkt angelangt sein)- we need a complete redesign from the beginning.
The origin of this phrase comes from a game, most likely Snakes and Ladders, where an unlucky turn sees a player returning to an earlier square of the game, maybe even the beginning square – square one.
Idioms with similar meanings include back to the drawing board and start from scratch.