scan always states permission denied

I installed avast, obtain a trial license and wanted to test scan on particular files like eicar test file, but I get always permission denied. I also tried chmod 777 eicar.com, chown avast:avast eicar.com, sudo scan eicar.com, sudo /etc/init.d/avast start, always the same: permission denied

I installed avast, obtain a trial license......
what avast?