Protected Content Plugin registration loop

Like some others using this plugin, a form is not being loading when attempting to register for membership- simply a refresh of the registration page.

I have read every support question and all of the available documentation for this plugin. After following some links in the support threads, I found that community members with unrelated questions had the same problem.

On my test installation, there are no additional plugins. Under WP General Settings, Membership is checked. Can anyone identify what the problem might be?

The documentation is skimpy at best and doesn't address the issue. Response to questions on this topic are slow or incomplete.

I would prefer to use PC over Membership, but after two days of working on it without success, I am losing confidence that it is truly an improvement over its predecessor. I hope that adequate documentation and/or tutorials are on the way.