Actually I fixed the problem:
1. Open the .htaccess file in your site’s root folder
2. Add these lines:
Options All -Indexes
AddType x-mapp-php5 .php
AddHandler x-mapp-php5 .php
That did it for me. Let me know if this works for you.
Exact same issue here – odd because I was initially able to install the all in one seo package without any trouble. I’m wondering if that plugin is caused the issue – have you installed that plugin too?