I'm not sure if I am following you on this one. Are you talking about the PM Pager? The Pager uses the Private Messages MOD.
If so below is some of my experience with the pager.
When I (Admin) am the only one online, the only user the PM pager will see is me (Admin). What I do is open another browser. I use both Internet Explorer and Netscape for this.
To test your pager do this: create another user name. Open each browser, go to your forum's default.asp in each one, and then log in as a separate user name in each browser. Next, open up the pager and you should see both user names listed. If you don't, be sure to clear your each browser's cache, and then retry it.