182: Invalid @aside value

The aside metadata name is declared to prevent the automatic integration of an @aside.nml file or to link a file with content aside from the main content manually. However, the assigned value is neither off nor a link in your case.

Solution

Assign the value off to prevent the automatic integration of an @aside.nml file:

@ aside: off

Use an arrow before the filepath, if you want to point to a file with content aside from the main content manually:

@ aside: ->/columns/the-strangest-day.nml