Hi TedSwiss,
The only thing it could have been other than manually removing the plugin files, was the default root .htaccess.
Here is what happened : one of the htaccess directives in the plugin conflicted with your site and caused a 500 error (being already existing). Then, you manually removed the plugin files via FTP .. However, the plugin already wrote the new directives to the root .htaccess.
The directives (added by our plugin) will ONLY be removed when deactivating the plugin (not by manually removing it). The only thing that would have worked in this case, is if you had to manually delete/re-paste the default htaccess rules (as given in the readme file).
We are busy working on a fix to have our plugin function without any hickups in both new and existing Wp installations.
Once again, my apologies for the inconvenience.
Regards
R