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I did try to see the other post (http://stackoverflow.com/questions/32516859/getting-error-on-content-editor-after-upgrading-to-sitecore-8), but it was not helpful.

I did try to see the other post (https://stackoverflow.com/questions/32516859/getting-error-on-content-editor-after-upgrading-to-sitecore-8), but it was not helpful.

Finally Found Solution

1. I haven't checked the Sitecore logs, it was emitting errors like 'Unable to connect to [http://localhost:8983/solr], Core: ...'
2. Overlooked the Index Manager, Rebuild Job Running Status. It has some errors.
3. Another major thing I missed was, haven't created all the core's required in Solr.

I hope this may help someone, who is starting Solr!