I got the error when using my actual name (Mark Freedman) in the “Your Name” field. When I used the user name I created for this website instead (which happens to be my email address), it worked fine.
The version of CJT Free I was using before installing the Dev version, was version 7.1.1 (the newest version — I just recently started using it — starting July 24th). I actually had to remove that plugin folder altogether before installing the Dev version, because the plugin failed updating directly (the error message said the directory was already being used, or something similar). I assume that was probably because I was trying to install an earlier version (Dev 7.1) over the version I already had there (Free 7.1.1)?