The code on click after update is fine, but when i click on the

The following code is used on a button click that should display when a date is available for reservation based on the data in my tables and form. However, when I click on the button nothing happens (event) ...It doesn't even display an error message. Any reasons why this is happening?

Public Function IsAvailable(roomName As String, Optional dt As Date, Optional t As Time) As Boolean
Dim sSQL As String
Dim rs As DAO.Recordset

sSQL = "SELECT * From ScheduledVenues WHERE VENUEname = '" & roomName & "' AND scheduleDate = #" & _
dt & "# AND scheduleTIME =" & t & ";"
'Your sSQL would actually be customized according to which controls were
'populated on the form. Do that by checking if the control is Null or "", add
'criteria where the controls are not Null or "".
Set rs = Currentdb.openrecordset(sSQL)
If Not (rs.EOF And rs.BOF) Then
rs.MoveLast
rs.MoveFirst
End If

If rs.RecordCount >0 Then
'The venue is scheduled for that time and date
IsAvailable = False
Else
IsAvailable = True
End If

If Not IsMissing(dt) Then
'include dt expression in WHERE clause
End If

End Function