After upgrading from odoo 8.0 to 9.0 I get following error, when trying to access any purchase order:

Odoo Server ErrorTraceback (most recent call last): File "/opt/odoo-filesystem/odoo/openerp/http.py", line 659, in _handle_exception return super(JsonRequest, self)._handle_exception(exception) File "/opt/odoo-filesystem/odoo/openerp/http.py", line 696, in dispatch result = self._call_function(**self.params) File "/opt/odoo-filesystem/odoo/openerp/http.py", line 332, in _call_function return checked_call(self.db, *args, **kwargs) File "/opt/odoo-filesystem/odoo/openerp/service/model.py", line 118, in wrapper return f(dbname, *args, **kwargs) File "/opt/odoo-filesystem/odoo/openerp/http.py", line 325, in checked_call result = self.endpoint(*a, **kw) File "/opt/odoo-filesystem/odoo/openerp/http.py", line 975, in __call__ return self.method(*args, **kw) File "/opt/odoo-filesystem/odoo/openerp/http.py", line 525, in response_wrap response = f(*args, **kw) File "/opt/odoo-filesystem/odoo/addons/web/controllers/main.py", line 897, in call_kw return self._call_kw(model, method, args, kwargs) File "/opt/odoo-filesystem/odoo/addons/web/controllers/main.py", line 889, in _call_kw return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs) File "/opt/odoo-filesystem/odoo/openerp/api.py", line 250, in wrapper return old_api(self, *args, **kwargs) File "/opt/odoo-filesystem/odoo/openerp/api.py", line 354, in old_api result = method(recs, *args, **kwargs) File "/opt/odoo-filesystem/odoo/addons/mail/models/mail_thread.py", line 369, in fields_view_get res = super(MailThread, self).fields_view_get(view_id=view_id, view_type=view_type, toolbar=toolbar, submenu=submenu) File "/opt/odoo-filesystem/odoo/openerp/api.py", line 248, in wrapper return new_api(self, *args, **kwargs) File "/opt/odoo-filesystem/odoo/openerp/api.py", line 490, in new_api result = method(self._model, cr, uid, *args, **old_kwargs) File "/opt/odoo-filesystem/odoo/openerp/models.py", line 1567, in fields_view_get xarch, xfields = View.postprocess_and_fields(cr, uid, self._name, etree.fromstring(result['arch']), view_id, context=ctx) File "/opt/odoo-filesystem/odoo/openerp/api.py", line 250, in wrapper return old_api(self, *args, **kwargs) File "/opt/odoo-filesystem/odoo/openerp/addons/base/ir/ir_ui_view.py", line 933, in postprocess_and_fields self.raise_view_error(cr, user, message, view_id, context) File "/opt/odoo-filesystem/odoo/openerp/api.py", line 250, in wrapper return old_api(self, *args, **kwargs) File "/opt/odoo-filesystem/odoo/openerp/addons/base/ir/ir_ui_view.py", line 476, in raise_view_error raise AttributeError(message) AttributeError: Field `minimum_planned_date` does not exist
Error context:
View `purchase.order.form` [view_id: 656, xml_id: purchase.purchase_order_form, model: purchase.order, parent_id: n/a] 

Can anyone explain to me what this error means and how I can resolve it?
I already removed every module that is not covered by the upgrade. I also verified that in table ir_ui_view for the record with id 656, there is xml data that includes a field falled minimum_planned_date and there's also an attribute minimum_planned_date in the purchase_order table.

I read somewhere that with odoo 9.0 minimum_planned_date is renamed but shouldn't that have been updated during the upgrade? Can I do that manually?
I upgraded multiple other odoo databases and never encountered this error before.