Upload PDF : example invoice-cmis

Hello,

I try to run this process. Invoice-cmis
When I start a new process in tasklist, it seems there is a problem with upload :

I got a broken image :

and when I click on “Start” button, I got this message : The process could not be started. : camForm submission prevented and a mention : This field is required.
image

I founded no trace in catalina.out

How can I investigate ?
Thank you for your help