Hi @nachtmahr ,
It sounds like your Windows Integrated Authentication is broken. This is an operating-system level feature, and the only thing you can do in ProGet is turn it on, or turn it off.
WIA is pretty buggy these days, and sometimes it just breaks. Here is more information:
https://docs.inedo.com/docs/installation/security-ldap-active-directory/various-ldap-integrated-authentication
Hopefully just doing a reboot of the server will fix the problem. If not, then you'll have to troubleshoot it, which kind of sucks:
https://docs.inedo.com/docs/installation/security-ldap-active-directory/various-ldap-troubleshooting#integrated-authentication-not-working
Note that you can disable WIA by using the Locked Out protocol:
https://docs.inedo.com/docs/installation/security-ldap-active-directory/various-ldap-troubleshooting#locked-out-restoring-default-admin-account
Hope that helps,
Alana