Hi Guys, there was another closed topic about this one. I couldn’t reply on that one, because it was closed already. I could solve the problem so I’m posting here. May help someone too.
Try to login to https://appstoreconnect.apple.com/
If you can’t, ask for the person in your company that enrolled the Apple Dev Program to try and add you as App Manager
After that probably the login in application loader will work (at least worked for me!)