I have LimeSurvey Version 2.06+ Build 150611. From tutorials, I understood that click + symbol to add subquestion. But In my case, the "+" , "delete" symbols is not active to click, I can type into the text box but save button is missing.
Also I have noticed that the layout of the page where the subquestion to be added is irregular for viewing. I attached the screenshot.

Delete whole browser history / cookies and try again.

I have already done the same. Now I have checked from another desktop(to ensure whether it is due to cookie/history) in the intranet. But no change.

Is there any error in console network tab while loading files?

What is console network tab? I dint get you. Is this related to limesurvey application or something else?

Browser developer tools...

Please go through the screenshot attached

problem seems to be with 500 server response but I dont have much idea why you are getting 500 response .. hope other experienced people here will help you out soon..

Remaining forms works perfectly. Only this form makes the issue.

Are there any JavaScript errors in the Console (not the Network) tab?

vilbiraju wrote: I have LimeSurvey Version 2.06+ Build 150611

Since 2.06 is now stable it could be a code base problem too. I'm not sure if 2.06 is really stable. Might only be a browsercache problem when using 2.05 and 2.06 at the same time. The screenshot shows that the css isn't really applied in the browser window. I had he same behaviour when installing 2.06 stable from scratch. Which version is your browser. Check firefox and chrome.
Are all browsers showing this misbehaviour?

There is a new build available:
Changes from 2.06+ (build 150611) to 2.06+ (build 150612) Jun 12, 2015
-Fixed issue: Unable to add answer options/subquestions or to edit quotas (Carsten Schmitz)

I don't think that version will be offered via online update at the moment.
There seems to be no way to choose a branch, which would be a good way to improve participation with beta,RC etc.
Stable, Release, Current and Edge (RC and Beta) could be a classification for different branches to update Limesurvey.
That way more people would update (the problems with going back in versions could be blocked).