In your form you'll need:
1:
Dim WithEvents dsOrder As AccpacOE1100.ACCPACDSControl
2:
Private Sub AccpacOE1100UICtrl1_OnUIAppOpened()
With Me.AccpacOE1100UICtrl1
Set dsOrder = .UIDSControls("adsOEORDH")
End With
End Sub
3:
Private Sub dsOrder_OnRecordChanged(ByVal eReason As AccpacCOMAPI.tagEventReason, ByVal pField As AccpacDataSrc.IAccpacDSField, ByVal pMultipleFields As AccpacDataSrc.IAccpacDSFields)
if dsOrder.Fields("CUSTOMER") <> "" Then Me.chkMyCheckbox = True else Me.chkMyCheckbox = False
End Sub