Why is there the restriction on showing the system.user in a datagrid? Don't really understand it. It used to work fine with 126.96.36.199 and since the 2.5.3 update mendix returns an error message. After all the system.user is displayed without any problems in a dataview. Why not keep it easy and user friendly by allowing to display in an overview (datagrid)?? I know I can use virtual attribute to display it but this is just additional work for something that used to work out of the box.
Why not creating a user object which is a generalization of system.user. Then you can everything what you want.