Hi Nico,
from this error log we can see, that the user, with the {SystemRole(s)} performs a change on the attribute '{Attribute}' of Entity {Module.Entity}. If the change is not performed in System Context, module roles (and therefore implicitly the respective user roles) need write access to the attribute. Otherwise Mendix will not allow the change and throw this error.
You can check the access rights in your Domain Model for the respective Entity and attribute.