Aí mesmo na sua captura de tela: " O servidor está configurado para aceitar conexões somente de contas com credenciais do Windows. ".
Gerenciador do IIS de nível principal > Serviços de gerenciamento > Permitir credenciais do Windows e do IIS
Referência: link
Além disso, verifique se você adicionou o usuário aos usuários do Gerenciador do IIS no nível do servidor e às permissões do Gerenciador do IIS no nível do site:
Nível do servidor:
Níveldosite:
E, finalmente, verifique esta página: link
ERROR_USER_UNAUTHORIZED
Diagnosis - This error code can surface because of a number of different reasons. It typically indicates an authentication or authorization problem, and can happen because of any of thee following reasons:
User does not exist
User does not have IIS Manager access to site if connecting using Web Management Service
Site does not exist
Password is incorrect
Resolution - If connecting using the Web Management Service:
Verify that the username and password are correct
Verify that the site exists
Verify that the user has IIS Manager Permissions to the site's scope
Resolution - If connecting using the Remote Agent Service:
Verify that the username and password are correct
Verify that the user account you specified is a member of the Administrators group on the remote computer. NOTE: If you are not using the built-in administrator, create a new group called the "MSDepSvcUsers" group and add your new administrator to that group.
Verify that the site exists