P9 - Non-existent property

Most problems are detected when Inform translates the source text, but this is one of the exceptions, a "run-time problem" which emerges only during play.

This run-time problem is not often seen, and is probably a symptom of something more peculiar having happened - if there have been earlier run-time problems in the same run, fix those first.

You appear to have tried to read or write a property. Properties are identified internally by a code number, but the code number you tried to use is one that does not seem to exist.