I have a contract law question that I'm hopelessly stuck on.
There is a condition of the contract (in this case, the monthly check-up on the machine by a professional) that could not be fulfilled, because the claimant restricted it from doing so (in this case, the owner of the business denied entry to the technician).
The claimant did so because they believed the defendant failed to uphold their side of the contract (the machine turned out to be faulty after six months) and now refuses to pay the money due for the cost of the machine.
You are dealing with the issue of anticipatory breach. The general rule is that there is no requirement for the claimant (the innocent party) to act reasonably to accept the breach ( faulty machine), the onus is for the party in breach to show that the innocent party has no legal excuse to terminate the contract and there is also a duty on the part of the innocent party to mitigate the loss.