Hello Aditi,
If you are using Google Chrome to test the App builder, it seems that there have been some libraries that have been removed from Chrome's DOM API in a recent update, and that may be causing this issue:
https://code.google.com/p/chromium/issues/detail?id=347506
To solve it, I added code with the definition of createAttributeNS and setAttributeNodeNS from here:
https://gist.github.com/arv/9529994
To file datajs-1.1.0.min.js placed inside appbuilder-1.0.1249\lib\onyx\util folder.
Hope this helps!
Regards!
Edgar.