Hi,

In the your system, there might be using some custom modules you have developed or taken from odoo apps. The issue seems to be coming from the custom code.

In the error message you can see the code,

if to_date < best_finished_date:

In the above code, the value coming to the field to_date is False, that is why you get the error. Check your system and see where the above line of code exists and update accordingly.

Thanks

I have no custom code in my installation.

Also i found that when i disable workcenters in the mrp settings, finish a production order and then re-enable the setting, the planning button works. Maybe its an initiation thing?