This particular error can happen for a number of reasons, though it's typically related to design elements.

First, check targeting and security on the part, page and template. Ensure the View is set to everyone. If this is confirmed, review the below information. 

There may be a number of customizations on the NetCommunity site that are prompting the templates to drop the CSS, which causes the incorrect template to be displayed. 
 
A designer will need to review the site further in reference to the following items:
  • CSS should only be in Style Sheet, none in Layouts
  • Check for both formatted & unformatted parts on the page that may contain custom styleing
  • No External References in Style Sheets, including fonts, pictures or other style sheets
  • No JS in layout
  • No Flash references
See this article for more to consider when designing the secure payment page.
Payment page for event registration or donation form is not showing the correct template