Ya and just on the main window is the license status. In the below screenie, it shows the expiration of license
That pop-up should be for virus defination updates or engine updates. I am using a trial version just now, so I don't get engine updates.
If you hover your mouse over the system tray icon, you can see something like "ESET Smart Security TM 3.0.566.0 Virus Signature Database: 2857 (20080207)"
Just note this number and cross check it after you get that pop up.