Error in the Accounting Method - payables

Hello, I need to edit the accounting method, I want to add a new event class "Payments" and a new rule set attached to it. I already put an end date for the old event class which is "1/1/1951", and adding a starting date to my new event class as "2/1/1951".

But this error pops up and I can't save or activate the accounting method or anything.

Please advise

Thank you

Victor Chrabieh