Can't preview my first form

Just purchased Gravity Forms, built my first form, when clicking the prevew button, get the following error messages:
Warning: require(./site/wp-blog-header.php) [function.require]: failed to open stream: No such file or directory in /home/athertch/public_html/site/index.php on line 17
Warning: require(./site/wp-blog-header.php) [function.require]: failed to open stream: No such file or directory in /home/athertch/public_html/site/index.php on line 17
Fatal error: require() [function.require]: Failed opening required './site/wp-blog-header.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/athertch/public_html/site/index.php on line 17
Troubleshooting:
1. I deativated my WP child theme, activated the default Twentyeleven them, when I click on preview, get the same error message.
2. I deativated all plugins except Gravity, when I click on preview, get the same error message.
What next?
thanks, Tablelands