Startup error message: Type Error NoneType object is not subscriptable

Have been seeing this error a LOT lately when opening certain .toe files.
Can anyone tell me what this means, and whether I should ignore?

Hi,
This might occur due to a number of factors including cloning operators, external tox’s or extension initialization order. Could you provide an example to support@derivative.ca so we can diagnose?
Thanks,
Rob.

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