A, B, C and D organise a chalet. Total cost of the chalet is $108, which is shared among the four friends. The $108 is first paid for by A.
B and C return $20 each to A at the beginning of the chalet.
Friends order pizza for dinner. The cost of the pizza is $40, which is paid using the money that B and C had returned A. So now, the total cost of the chalet has been increased to $148 (each should give A $37, except for B, for A owed B $7 beforehand)
So later, B returns A $10, C returns $17, D returns $37. In total, A has $64 collected from the rest of us.
That's when we ran into trouble. Because A should collect $111 from us, if we go by the each-person-pay-37 theory. So it doesn't make sense.
Edit: Never mind, A gets it now! :D