Just doing a bit of brainstorming here...
...could the fact that the site I am trying to install PowerCMS on was written in HTML5 be part of the problem?
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.