Dear All,
Finally we were able to resolve this concern by following the below steps.
1.) In the chrome browser, we have used the developer tools and we have found out the exact error. Please find the attached screen shot for same.
2.) Upon checking, we have found that the portal URL which we were using in the browser was not a fully qualified domain URL wherein we were using the URL in below way
Portal URL - http://xxxx:52600/irj/portal
Host in the backend - xxxx.aaa.co.bb
3.) When we changed the portal URL to http:xxxx.aaa.co.bb:52600/irj/portal, it has started working and we were able to access the external catalogs.
Best Regards,
Bharathi