What_does_the_error_message_'arguments_from_operator_*_have_incompatible_shapes_while_getting_result'_mean?

This would happen when, e.g, you try to multiply a 20x20 value with a 20x10 value (how your nodes end up with something like this I do not know...) The shape of each axis must be equal, or else one can be equal to 1.