I don't have time to look at the sample right now, but here's the full code from above, which changes or eliminates the grouping based on user selections (an option group on a form). Post back if you're still stuck:
Code:
Private Sub Report_Open(Cancel As Integer)
Select Case Forms!frmReports.fraGrouping
Case 1 'sort/group on car type
Me.GroupLevel(0).ControlSource = "CarType"
Me.txtGroup.ControlSource = "CarDesc"
Case 2 'sort/group on company
Me.GroupLevel(0).ControlSource = "Company"
Me.txtGroup.ControlSource = "Company"
Case 3 'sort on date/time, no grouping
Me.GroupLevel(0).ControlSource = "DispDateTime"
Me.txtGroup.ControlSource = "DispDateTime"
Me.GroupHeader0.Visible = False
End Select
End Sub