The screenshot of the error is attached. The link in the screenshot points to the URL http://docs.moodle.org/en/error/moodle/dmlwriteexception .
What could be the problem here?
This issue was created at http://tracker.moodle.org/browse/MDL-24339 . At one stage, 1.95 to 2.0RC1 upgrade was working but at this very moment using the latest build of 2.0RC2, 1.95 to 2.0RC2 upgrade is giving error which also I have put up in the tracker under the same issue. Let me know if there is a need to create a new issue for that.
Manish, thanks for creating MDL-24339 and for your detailed feedback. Sometimes a discussion in a tracker issue becomes longer than a discussion in a forum!
Regarding whether to create a new issue or not, if an issue is resolved and then the problem reoccurs, you can either create a new issue for it or add a comment requesting that the issue is reopened.