Hi,

I've seen a lot of odd behavior in the past with configurations/misconfiguration dealing with message notification.  Check this user's configuration for any message notification settings.  If you don't see anything configured for him, then it'll probably be difficult to track down what's happening, especially if it's intermittent and if you're not able to find a pattern.  The easiest way would be to ideally have Port Status Monitor open when it's making the call, but that's not easily done when you're not sure when its going to happen.  The best place to start would be to check the configuration for this user, then if that doesn't provide any help, set the Macro traces for Notification problems.  Once you've experienced the issue, Gather Logs>Select Logs and choose the AvCsMgr and AvNotifierMgr components for the timestamp that the oudial notfication happened.

Hope that helps,

Brad