1. Have you checked in your usergroup permissions have you set the setting to allow posting files directly to server as YES? that needs to be set correctly as essentially what flash uploader does is it bypasses http upload prompt so its like allowing bulkupload access
Next if that does not work the flash uploader does not work for everyone. One issue found is that you may need to if allowed to create an .htaccess file and stick SecFilterScanPOST Off in it. Or contact your host to see if mod security is on and if it can be disabled.
The flash uploader won't work if you are using apache with mod_security on - the above fixes the issue.
2. Lightbox is only contained in Photopost Pro not vbGallery.