Article conversion error S1121 when opening an article in Content Station 9

Issue

When opening an article in Content Station 9, the following error message appears:

Article Conversion to WCML Failed (S1121) error

Analysis

The following error is also logged in the Server logging:

Uncaught JavaScript exception:

ReferenceError: app.convertFile is not a function

Solution

Update the installed Smart Connection for InDesign Server plug-ins.