The prisons temperature is alright. Its also enclosed.
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Here is the splitted savefile part 1:
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Part 2:
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Found the culprit... Since the pawn is uninjured, uncheck the prisoner bed from medical.
A medical prisoner bed will only accept an injured pawn.
You're right Jimyoda. Thanks
So at least there could be a better fitting message telling you whats the problem. It's so confusing sometimes