Running on the Plus or original SE, Dark Castle requires the "alternate screen buffer" that is available on those Macs. This is not just some memory, but a specific 22KB of it.
If you use MultiFinder, or you have installed either AppleShare or MacsBug, this is no longer available for Dark Castle to use.
So, boot with extensions off and disable MultiFinder.
If you use MultiFinder, or you have installed either AppleShare or MacsBug, this is no longer available for Dark Castle to use.
So, boot with extensions off and disable MultiFinder.