here is an updated cop of the webassist/framework/library.php page that should correct the problem.
to control the allowed file types for uplaod, edit the webassist/kfm/initialize.php file.
the following line can be used to add banned extensions:
$kfm->defaultSetting('banned_upload_extensions',array());
for example, ban png and PDF files:
$kfm->defaultSetting('banned_upload_extensions',array('png','pdf'));