There is a plugin called WP-Ratings. It has worked well over the years until recently. It may have been as a result of a WordPress upgrade. Whatever the cause, WP-Ratings failed to work. The symptoms is that the rating stars were visible, until the user clicked on them. The ratings would become invisible or blank and result in an error message produced by Internet Explorer. The error had to do with prototype.js.php.
Since the plugin was a version or two behind, an update to the plugin to the most recent version in an attempt to correct the problem, did not correct the error. Updating prototype.js to the most recent version did correct the error and did not break anything else. The prototype.js version that was used was so old it is not even available in the prototype archives.