Hmmm...I totally forgot this one. Unfortunately there is no way to mark posts and topics as Unread, so I may forget answering to some topics from time to time.
About your question:
ScreenMask is initiated on client side as soon as an ajax event is generated. For technical reasons you can not initiate a screen mask from server side. You should bind a control to a UniScreenMask and each time that control generates an event a mask is displayed.
In demo project the Sleep() method is only used to emulate lengthy operation.