I encountered a similar error, however I wasn't using third party software. In my instance it was because the document had to be converted to a more current version, for whatever reason it wanted me toconvert the document and save it graphically before it would act upon it scriptually.
Hope that helps.
Hmmm. I don't know what "never interact" does, internally, but suppose you switched off user interaction and then a script calls "document.close". The three choices in the Save confirmation dialog are "Save:Yes", "Save:No", and "Cancel". Given that, it would be the safest to have it always return "cancel"!
Since this is a 3rd party plugin, you probably can contact its manufacturor and ask for a workaround, or possibly a modification.