A small update on the question:
The content is displayed if I give the startpath in the portlet configuration as the URL of a site e.g. \content\MyPage.html where 'MyPage' is a site. However, if I try to give the startpath as any of the childpages under the site 'MyPage' e.g. \content\MyPage\ChildPage1.html, it throws an error.
Hi Yogesh, actually I was trying to deploy the CQ Out of the Box Portlet (CQ Portal Director Portlet) on WPS 8. Anyway, through a lot of trial and error, I got the desired result.
The issue was with the structure. Since, the portlet has locales configured 'en', 'de' by default, it looks for the similar structure. Hence, one needs to disable the locale info add checkbox in the Apache Felix Web Console configuration.