[development] node_preview return access denied page

I am working on quiz questions import module. This module allows quiz authors to create bulk of questions from csv text files. I have no problem in creating questions node from imported file and saving it to database. I would like to show a preview of import question (which are nodes) before they get saved into database. Node object generated from file looks like http://drupalbin.com/10639 . When i call node_view or node_preview with this node object it returns access denied page. Is there anything i need to do before calling node_preview ? Any help will be greatly appreciated. -- Thanks Sivaji