Hi.
Just a thought. I'm no expert and I haven't tried this exact scenario, but I have used similar workarounds myself. It may work trying to? create a new block just before the before the platform turnout with virtual signal masts controlling entrance to this new block. The signal mast logic would need editing to protect this block only if both platforms were occupied? (perhaps using? a virtual sensor and logix). The train would stop at the signal and wait before entering the block, presumably before before triggering the pop-up message box. It? would only then proceed after one of the platforms became clear, negating the popup.
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Steve 009 in UK