It changed in recent ToscaWidgets versions, when you want to display a widget (like the DataGrid) you should prefer an explicit call to the display
method instead of calling the widget itself.
try to replace ${grid(value=data}
with ${grid.display(value=data}
Have a look at the Forms tutorial, it covers some basics on working with forms and TW2 widgets, the DataGrid in the ends it's just a Widget so behaves like forms for some features.