Got more clue yesterday, comparing the backup wiki xml file done from moodle version 2.8 and version 3.3 I've noticed that the xml created by version 2.8 got problem with the content element. (as in the attached pic)
While from 3.3 the content element is complete ... got the open tag and close tag.
Is there any issue with 2.8 backup program ? huhu ... need to dig deep now.
Any help is much appreaciated.