Hi I ran the same datas and more or less the same setting before with out error (skip 4368 lines of hourly weather data file to simulate from July) How should I understand this message? thank you Xavier ***** ERROR ***** TRNSYS ERROR # 188 UNIT 5 TYPE 56 MULTIZONE BUILDING INTERNAL ERROR IN SOLAR RADIATION DISTRIBUTION (SUMSITOT) OF 20.212 % AT TIME 4376.00