ToolBar Button Problem

[goraya]

Hi
I am working with a toolbar in MSworld (Access). I want that when a button is pressed it remain pressed untill an other button is pressed. Here is the code

Private Sub btnPressed(ByVal btn As String)
Dim ctrl As Button

For Each ctrl In Toolbar1.Buttons
ctrl.Value = tbrUnpressed
Next

End Sub

if a button is passed as an orgoment it display error message Type Mismatched.
Waiting for help................
Tanks in Advance