From the message of Enkonyito posted just before yours, sky lighting is implicitly enabled and non-editable in aerial view while it is disabled in virtual visit. So you should use Virtual visit mode to unselect this checkbox.
For your information, Enkonyito requested to disable his account on this forum and at SourceForge.net. This probably means that we won't see him contributing to Sweet Home 3D anymore!
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Emmanuel Puybaret, Sweet Home 3D creator
