Odd enough I just recently answered this question. The SEOmoz crawler is correct, because without a redirect you will be able to access both versions of the page in your browser.

www.yoursite.com/

www.yoursite.com/index.html

To resolve this issue simply rewrite the index.html to the root url by placing the following code into your .htaccess file into your root directory.

Options +FollowSymlinks                                                                                                            RewriteEngine on

Index Rewrite                                                                                                                                RewriteRule ^index.(htm|html|php) http://www.yoursite.com/ [R=301,L]                                      RewriteRule ^(.*)/index.(htm|html|php) http://www.yoursite.com/$1/ [R=301,L]

You can also do the same with the index file in any subdirectories that you might create, by simply placing a .htaccess into those sub directories and using variations of the above code. This is how you create nice tight URLs without the duplicate content issue that look like - http://www.semclix.com/design/business/

Here's the .htaccess rewrite command that you can use for the index.html redirect -

Options +FollowSymlinks                                                                                                   RewriteEngine on

Index Rewrite                                                                                                                   RewriteRule ^index.(htm|html|php) http://www.amarasoftware.com/ [R=301,L]              RewriteRule ^(.*)/index.(htm|html|php) http://www.amarasoftware.com/$1/ [R=301,L]

We set  up our site to utilize a index redirect for all of our sub directories as well, so with this method you simply name your sub directories to match the url path that you desire. Each sub directory has it's own index which you redirect with a variation of the above code. By doing this you can have nice clean url paths like http://www.semclix.com/design/ecommerce/ - and mitigate the duplicate content issue. We hope that this helps.