thanks for the reply I found another way to accomplish what I was after..
Private Sub cboVendor_GotFocus()
If IsNull(Me.cboComponent.Value) Then
Me.cboVendor.RowSourceType = "Table/Query"
Me.cboVendor.RowSource = "tblVendor"
Me.cboVendor.ColumnCount = "3"
Me.cboVendor.ColumnWidths = "0,0,1"...