Argument 7 passed to rules_action_mail() must be an instance of RulesState, instance of RulesAction given

Rules 2.0 has:

function rules_action_mail($to, $subject, $message, $from = NULL, $settings, RulesState $state, RulesPlugin $element)

and the new Rules 2.1 with i18n has:

function rules_action_mail($to, $subject, $message, $from = NULL, $langcode, $settings, RulesState $state, RulesPlugin $element)

so the function signature has indeed changed. So we need to find where rules_action_mail() is being called and add an additional argument at position 5 for $langcode.

Looks like the function calls are stored in the serialized Rule data in the database. So we need some code to update that data to add in the additional $langcode argument for previously-stored rules.

Thanks! The fix was as simple as that. Odd, as I thbought the caches had been cleared, but I can't have done.