Try messing around with the OnBeforeChange event for the repeating group (go to data source >> double click on the group >> go to validation and event handlers tab >> select the OnBeforeChange event and press edit). In the event handler, check the count and if it is too large set eventObj.ReturnStatus = false.
If eventObj.IsUndoRedo = false AND eventObj.Operation = "Insert" AND CHECK COUNT HERE Then
'too many items
eventObj.ReturnStatus = false.
End If
Hope that works...that is what I would try...
Jason
http://www.k2distillery.com/