I’ve just seen this error message twice in a few minutes:
I’ve been using Notes 8.5 since January and have never seen this exact error before today.
Both times, the error occurred when I used the shortcut Alt+2 to activate the second action button on a view.
This action uses a @Command([Compose]; …) formula to compose a new document with a specific form.
Upon pressing Alt+2, the form opened in the client, then the error message appeared a moment later.