Why Safari keeps demanding proxy authentication?

Hello everybody,

I have configured Safari to use a Proxy server, the same as all other computers in our network.

At the proxy settings for the USB Ethernet connection I have enabled only Web Proxy and Secure Web Proxy (HTTPS). Also the option Use passive FTP mode (PASV) is checked.

Each time Safari is opened it asks for authentication saying: Username and password... you entered was incorrect.

The user enters the credentials for proxy authentication. Immediately Safari asks again for credentials. Even when we check the option "Remember this password in my keychain" Safari continuously keeps demanding authentication.

At this point we decided to press Esc for the authentication windows. Several times. At the end, the web page is loaded correctly. This is wired!

In the meantime we have checked and updated the MacBook.

Also, interesting to know that we have installed Mozilla Firefox and it runs fine after one time authentication.

Do you have any idea how to solve this?

Thank you in advance,

AL