authentication as root fails

I have a simple online installer with a script in its data directory. The goal is to have the script download a packet, via wget, unzip, and copy to the /opt/library directory. In order to simplify testing, I have reduced the script to just copy some files unpacked with the script to /opt.
As you will see from the pictures, the installer starts normally, requests password, but then return the error on picture 2. From there, the behavior is inconsistent....
After pushing "OK", the installer sometimes continues and gets stuck;
other times it just mentions a problem elevating user privileges.