Ok, we’ve have resolved the problem. I’d like to give some tips to other users:
1. Avast Web Shield was causing problems, disable it.
2. This plug in does not give errors when image formats and sizes are not compliant with the form config, really need to add error messages.
3. Make sure your YouTube account has at least one channel, otherwise YouTube upload will not occur
This is a great plug-in, but need to take care of details.
Thanks for this plug-in