[wix-users] session.Message in custom action called from Dialog?

[Stephens, Rich]

So, I am trying to validate my custom configuration dialog.

<Control Id="Next" Type="PushButton" X="236" Y="243" Width="56" Height="17" Default="yes" Text="Next">
<Publish Event="DoAction" Value="ValidateConfigSettings">1</Publish>
<Publish Event="NewDialog" Value="VerifyReadyDlg">CONFIGSETTINGSOK=1</Publish>
</Control>

I am calling a c# custom action to do validation when the "Next" button is pushed.

Here's where I'm calling session.Message in my "ValidateConfigSettings" custom action:

Record record = new Record();
record.FormatString = errMsg.ToString();
session.Message(InstallMessage.Error |(InstallMessage)System.Windows.Forms.MessageBoxIcon.Error |
(InstallMessage)System.Windows.Forms.MessageBoxButtons.OK, record);

Everything is working exactly as desired.  The dialog doesn't continue if there's an error, etc, but... the message box doesn't appear.

Am I missing something?

Rich