Trying to upgrade "Protected Content" and get an error

Our protected content plugin broke due to being old (receiving 403 errors), and I see that you’ve released “protected content 2”. According to your update instructions, you install it and it silently upgrades the old version. In order to fix their site, we purchased the plugin. Unfortunately for us, we encountered this error upon activation:

Fatal error: Cannot redeclare class MS_Plugin in /home/thewedne/public_html/wp-content/plugins/protected-content/protected-content.php on line 132

I have searched out your forums and it looks like other people were having the issue I was having before we upgraded. It seems like you guys are helping people specifically with their needs. I can provide FTP details, but I think this ticket is public so let me know how you want me to get those to you.

We have had to temporarily delete the membership plugin so the site works. Do you know what is causing this and how it can be fixed? Thanks!!