More information is required. Are you using the Kaltura SaaS or is this self hosted? If SaaS, please open a ticket with our support team. If this is self hosted, please state which interface you are using to perform the upload, I assume you're using KMC? While trying to upload, please open the browser's dev tools and look for errors under the "Network" and "Console" tabs and, from the server's root shell, run:
Look at the errors being outputted to STDOUT and paste them here.