Final answer:
The scenario without a binding agreement due to problems with consideration is C) John's promise to pay Eric for past work. 'Consideration' must involve an exchange of value for something new, not for benefits previously received.
Step-by-step explanation:
When considering which of the given scenarios would not result in a binding agreement because of an issue with consideration, it is C) John tells his neighbour, Eric, that he will give him $30 to show his gratitude for Eric's extraordinary work for Little League. This scenario lacks the necessary elements of consideration because it is an attempt to pay after the fact for a benefit already received, also known as a past consideration, which is not enforceable. The other scenarios listed involve valid consideration: A) represents a modification of an existing contract with new consideration; B) involves a nominal consideration, but still a legally sufficient one; D) is a promise under seal, which traditionally does not require explicit consideration, and E) represents accord and satisfaction, where a lesser amount is accepted in exchange for an early payment, altering the terms and creating new consideration.