I'm not adding the DropDownDataGrid manually. I explained in my previous post, the page already generated with a form and inside the form there are the table's fields.
When I click the button to edit the "Fields" in the property, then a dialog popped up.
In this dialog I change the type of ClientNID field from 'integer' to 'lookuppopup' and supply the properties accordingly: "Data", "TextProperty" and "ValueProperty".
And yes, I defined the relationships between the related tables in the database.
Still got the same error message above. And I'm using the latest update (ver 2.56.4).
Btw, I can use 'lookup' to another table even without relationship if the table not to big. In my case, the user table is about 2000 rows (can use lookup), but not client table (about 200000 rows).
Edit: FYI, the client table have a lot of fields (not only a lot of rows) but I only show 3 fields to the lookup (as the screenshot before).
It's my chrome's developer console screenshot:
Thanks