I found my problem and my solution: I have data stewards that are "owner" of data, and on some forms, i wrongly created a link that connects with the system.owner/full name attribute instead of linking over my data steward owner.
Showing the system fields createdBy or owner as attributes on a form causes this kind of problems when creating and/or saving records.
(For more info: see https://forum.mendix.com/questions/7/Created-by-and-last-changed-by ).
Which context are you using? Does the specific context that you are using belong to a user that has read/write access?
This also occurs every now and then when I have preliminary security config like admins = full access to everything, user = limited access for all users. Very strange: it occurs to admins, as Eben, with full access permissions.
I ususually later refine the security, and the error behaviour then dissapears, so I didn't troubleshoot this yet.
I don't change system fields. However, I have a boolean "IsDirty" attribute that is set true by a Microflow by On Enter or On Change events, and that is reset to false in a before commit event. Could that be causing it?
Working with version 3.2.1.
Ok i have solved the issue. Something i have overlooked.
One of my fields tried to change the ChangedBy attribute of Mendix which i presume and believe is fatal.
I have changed it so it points to my Agent_Lead Attribute Association and it works fine.
Thanks for your feedback.