This error usually means the user does not have permission to create a new FileDocument (or your custom file entity).

The File Uploader widget always tries to create a new object in the background. If the user role does not have create access on that entity, you will get an error like “Action create new files”.

I would check the following:

First, go to your file entity (e.g. System.FileDocument or your custom entity) and verify that the user role has Create and Write access.

Second, check entity access rules and make sure the user can at least create the object without restrictive XPath constraints.

Third, if you are using a custom specialization of FileDocument, make sure the module role is correctly mapped to the user role in Project Security.

In most cases, fixing the create permission on the file entity resolves this issue.

If this resolves your issue, please mark it as accepted.

That sounds like you may not have a microflow / nanoflow setup to create a FileDocument or Image specialisation object when the file is updated.

https://docs.mendix.com/appstore/modules/file-uploader/#action-to-create-new-files

If it is in place, then check that you have given your user the correct role with permissions to create the object and run the microflow / nanoflow.

I hope this helps.