I am sorry to hear that you're having troubles with installing your Network Solutions certificate. After researching I found that you actually have the same certificate installed on both your sub domain and your www. domain. If you visit your site using a browser like Google Chrome you will see an error stating that the site is identifying itself as www.domain.com. This means you have the www. certificate installed on both your domains.
I also used an internal tool to check the Certificate Chain and it did show that the certificate installed was for www.domain.com.
If you cannot figure out how to do this the way you have planned I would suggest contacting the server manufacturer for the best instructions.
Hope that helps! Good Luck! (IMG:http://forums.networksolutions.com/style_emoticons/default/thumbsup.gif