Macro Error when running Export InDesign Tagged Text script

I have recently been using Toshi Omagari’s script to export a full set of glyphs in a font. It’s been great. But today it started giving me this error and I have no idea how to address the underlying issue. Does anyone know what to do to clear out the export error?

One file is working fine, while another is giving this error.

Doney the font have any instances?

No. The file I am having trouble with only has a single master and no instances.

You need at least one instance. Add one and don’t change anything in it.

That worked! Thanks so much!