Hello @MarcC60. I'm sorry that you're experiencing this issue when trying to upload your contacts.
It does sound like you might be experiencing a browser issue. Have you tried using a different browser or an incognito/private window to upload your contacts? If you are able to load your contacts using the new browser or incognito/private window, there is probably an issue with a third-party plugin in your original browser. Please read this FAQ for information on disabling these plugins.