That's strange that he's getting that pop-up notice with BOTH definitions and program updates set to Manuel. Personally, I would at least set the definitions file to Automatic, BUT to deselect the Automatic Update "Show Sliding Box" if you don't want to be interrupted during your presentations. Keep this in mind, not just for Avast 4.8, but for 5.0 as well.
Seriously, you run a greater risk of infection by having manual updates at manual and messing something up than having the definitions file update automatically. I would still set the Program updates to "Ask When Update is Available." Set your Database Definitions to Automatic. You can make those changes, turn off the sliding box after automatic update, but at least you will be protected.
What element is distracting during your presentations? Is it the voice that announces the update or the sliding box itself? Your answers to these questions may help us to guide you in setting up the program. But I definitely would say, put the database definitions to automatic at least.
5.0 works great provided that you uninstall 4.8 first for best results. The default setting is what I use for 5.0, which is the same as 4.8 is the following:
1.) Update Virus Database......Automatic
2.) Update Program...Ask when update is needed
In terms of solving your problem with 4.8, have you tried uninstalling 4.8 and reinstalling 4.8 to see if that makes a difference? (Yes you would have to re-register your license key.) OR, you could just uninstall 4.8, get 5.0, after the AV updates, right-click on the Registration Tab, fill out the form, click submit, and get protected for 12 months.
Jack