This issue is solved now, I checked your other forum and there was the solution to disable "mod_security" and which I did with the help of Website hosting support team.

I was suggested by hosting support team to disable and enable whenever I make changes in the website. But that's an impractical and lenghty process so I asked for the better solution and I was helped by him, by whitelisting a particular rule which blocks the request from the website. Same you can ask from your hosting support team. This solution is safer then disabling "mod_security" all the time.

I am mentioning here so that others can have faster and proper guided solution to save their time.

I have a suggestion here - In most of the forus where problems are solved but those converstation are in hidden comments and also when your team fix the issue, sometime they don't mention what they did. So, my suggestion is that whenver the problem is solved there should be a detailed explanation which a non-technical person can understand then life becomes easy for us as client and also yours as support team.