(JoomDoc 2.0.2 ; Internet Explorer 8)

Frontend registered users can't go through the 3rd step of "submit a file" (whatever the previously chosen method is : upload a file, link a file...).
"Save" and "Cancel" buttons are inactive.
It seems there are errors in the page : detailed IE8 error log is attached.
(upload-rights are obviously correctly set)

Although I guess it's a commonly-used fonctionnality, I didn't find any post about such a problem.
Any idea ?