Classified latest 5.1
Spend 3 hours to find what's the cause but still got no clue
1. VB4 integration all of them is ON.
2. WYSIWYG and Standard Controls is ON at vBulletins Message Options
3. Allow Comments permission is YES on Classified Admin - Control Panel
4. Chrome, Mozilla, Opera all of them is the same blank white page on comment option.
5. Default vBulletin theme and custom vBulletin themes got same blank white effect.