The first error also happened to me. I'm using an VPN and it worked fine for me uploading files on itch.io directly, but it didn't work for butler transfer. I closed the VPN and tried uploading again, but it still won't work. I also tested my network connection, it was 37.1 Mbps upload, which should be fine. I don't know whether it's related to Internet firewall or something else. Has anyone solved this issue?