Hi, Vaishali
There are many pieces in play. updatemgr in dom0 is generating the
exception and sending it out over dbus, I think? I'm not sure if
xenmgr in dom0 is involved, but somehow the html/javascript in uivm
sees it. The javascript code in toolstack-data is what displays the
exception. I'm not sure, but the javascript may have specific code to
handle and display only certain messages. i.e. you might need to
modify that to show your message.
I hope this helps.
-Jason