Hi Vlk, As I have already rebooted & right click scanning is working fine, I cant tell you if on-demand scan would work during that problem.
But if you want, I can uninstall the antivirus and reinstall, & see if I am asked to reboot. If there is no reboot offered, then context menu scanning should fail and on-demand scanning can be tested. That is too little an effort if it helps, in return for such great service & product offered by you people.
Anyway, I wrote the original message ignorant of the fact that reboot was the necessary requirement and thinking that avast antivirus is designed to fully function without reboot as it did not offer me any. But it turns out that it is fully functional only after the reboot which is offered as default option. This might be something rare as in my case. But if you want to find out you can simply ask users( may be by vote) and get to know what percentage of users were not offered reboot.