Error: Argument 1 of Node.appendChild is not an object. (mendix.lib.XPathSource)
Users by default don't have any rights to view properties from the system.user entity (the Generalization that is most likely used for your Account object).
If you are filtering on any of those fields you need to either be an administrator with the right to manage users from all user roles or specific userroles (found in the project security when editing a user role).
We ended up resolving this error by removing the DataGrid where this was happening, and creating a new one that is exactly the same as the old one.
So it seems like our model was corrupt in this case.