The plugin, as part of automatically protecting comments from view, spoofs WordPress into believing that posts are password protected. Rather than actually setting a post password for the post, this is generated on the fly.
In some rare instances, this may cause the password protected dialog to display and request a post password (for which there really isn't one). This appears to be one of those cases.
For cases such as these, there is a filter hook in the plugin for the auto-generated post password. Using this filter hook allows you to return an empty value for the post password, which should return WordPress to believing there is no post password (which there really isn't).
Info on that filter and an example snippet is available in the Users Guide here:
(NOTE: if you are not familiar with using filters and action hooks in WP, snippets like this go in your functions.php file.)