Published but not published

[James Martin]

I`ve just published my first site using Sitebuilder - got the green light, everything seemeed fine.
When I checked it online, it`s just a liat of files under the heading Index of/
I looked through for errors and came across this;-Fatal error: Cannot instantiate non-existent class: sb_modules in /home/jmart57/public_html/newjpm-marketing.info/include/Modules/DownloadableContent.php on line 2
Any ideas how to cure it.