How do you create a waiting dialog in WIX?

I'm trying to create a dialog to display whilst the installer is checking an SQL server exists. I've used the following code:

<Control Id="Next" Type="PushButton" X="244" Y="243" Width="56" Height="17" Text="!(loc.WixUINext)">

    <!--Show Waiting dialog-->
    <Publish Property="SQLServerChecked" Value="0">1</Publish>
    <Publish Event="SpawnWaitDialog" Value="WaitCheckSQLServerDlg">
        SQLServerChecked = "1"
     </Publish>

   <!--Checks the SQL server exists-->
   <Publish Event="DoAction" Value="CheckSQLServerExists">1</Publish>

   <Publish Property="SQLServerChecked" Value="1">1</Publish>

</Control>

However my WaitCheckSQLServerDlg shows, never disappears and the Action CheckSQLServerExists doesn't get run. How would I alter my c开发者_JAVA百科ode so that the WaitCheckSQLServerDlg displays whilst the CheckSQLServerExists action is running?

Thanks