I too was having this problem. The "EDIT MORE" section would yield a blank screen.
I am proud of myself. I tracked down and solved this bug on my own 6.0.2 install.
In previewedit.php on line 61:
code:
if ($peditchange) {
It must be changed to:
code:
if ($ubbt_lang['PEDIT_CHANGE']) {
This allows the variable that the 'edit more' screen is passing to the previewedit.php script to be properly recognized.
Now I get no more blank screens, and the entire process works flawlessly now.
Hope this helps someone!