To fix this issue you need to:
1. Pick which version of the url you want to promote.
2. 301 redirect the version not being used to the one you chose.
The way you have it right now the site can be accessed with or without the www in front. If you leave it like this any incoming links pointing to your pages will be spread between the www and non www versions. To maximize the incoming links to a page you need to set things up so only one version of the page is accessible by everyone, including the search bots.