I was able to solve my original problem and advance to the next screen. It happened after I used my FTP File Manager on my cpanel to set the read and write permissions on the data folder (or maybe the virtual folder I'd set up in IIS with anonymous access and directory browsing blocked kicked in at that exact moment -- who knows?).
In any event, right after I was able to get past the dataroot error message, something bizarre happened. I received a 500 error message and now I'm in the same situation I was before with the "Dataroot location is not secure" message.
I've started a new post on this new problem at https://moodle.org/mod/forum/discuss.php?d=217679