I read though that thread, and the problem is that the installation program does not get far enough to create the C:\Program Files\Blue Iris Folder.
No folder present in Program Files or Program Files (x86).
I've downloaded the installation program several time to eliminate a download problem.
This was an initial installation of BI.
I downloaded the latest BI file in the Downloads section of this Forum, which is (I know now) just the update to BI.
That update, when executed, places the newer files into the existing BI directories, but since I had not run the actual installation program those directories were not there. Hence the Error.
Once I obtained the actual BI installation file, everything went smooth.