Ooo, good point.
Try the following and see if it works
Code:
Private Sub cboPropCode_AfterUpdate()
Dim strSource As String
Dim strSource2 As String
strSource = "SELECT DISTINCT Unit " & _
"FROM qry_Contacts " & _
"WHERE PropertyCode = '" & Me.cboPropCode & "' ORDER BY Unit"
strSource2 = "SELECT DISTINCT Tenant " & _
"FROM qry_Contacts " & _
"WHERE Unit = '" & Me.cboUnit & "' AND PropertyCode = '" & Me.cboPropCode & "' ORDER BY Tenant"
Me.cboUnit.RowSource = strSource
Me.cboUnit = vbNullString
Me.cboTenant.RowSource = strSource2
Me.cboTenant = vbNullString
End Sub