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.

When values are defined using a table, the columns of that table become properties. For instance, if the table defines colours and there is a column called wavelength, it then becomes legal to talk about the wavelength of blue (supposing that blue is one of colours defined).

Here, an attempt has been made to read or write such a property for something which cannot possibly be a qualifying value - for instance, the wavelength of -21 would be such a case, though many such mistakes are rejected at translation time rather than now.