Network Solutions (networksolutions.com)

1. After going through the first 3 steps indicated in this article in order to add your new subdomain, below are the following steps you need to take in the domain registrar before going back to finish the process and having your new subdomain in Instapage.
2. Log-in to your account at www.networksolutions.com and click Manage Account;
3. Click on the Edit DNS link under the My Domain Names section;
4. Click the Edit Advanced DNS Records link next to the domain you want to use with Instapage.  This will open the DNS Manager Settings page;
5. Scroll down to the section Host Aliases: CNAME Records, click the Edit CNAME Records button;
6. In the 'Alias' field, type the name of your chosen subdomain.  For example, if you picked lander.mydomain.com as your address, enter lander here. Or, if you're using a root domain such as www.mydomain.com then you'll want to enter www here;
7. Select the Other Host radio box and type secure.pageserve.co in the other host field;
8. Click Continue.  This will bring you to a confirmation screen (If you see the error "An A Record Already Exists for the Entered Alias" at this point, go here for instructions on deleting the conflicting A Record);
9. Confirm your settings and Click Save Changes.

For additional instructions see: http://www.networksolutions.com/support/cname-records-host-aliases/