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The problem appears to be with your thermostat setpoints, not the design days. The error says that your zone thermostat setpoints are 24 C for heating and 23.5 C for cooling, is that really what you intended?
You can't simultaneously heat to 24 C and cool to 23.5 C, the heating/cooling equipment would both turn on and fight with each other. The only way you could model setpoints like this would be to schedule the heating/cooling equipment so that they never run at the same timestep.