On starting the full crawl of the default content source i recieved the error.
The secure sockets layer (SSL) certificate sent by the server was invalid and this item will not be crawled.
It was because one of the site was ssl enabled.
Solved it in the following manner
Central Administration > Application Management > Search Service > Farm-Level Search Settings
On the Manage Farm-Level Search Settings page, in the SSL Certificate Warning Configuration section, select the Ignore SSL certificate name warnings check box if you want to trust that sites are legitimate even if their certificate names are not exact matches.