Problem with Proxy Server's Security Certificate

Hello,

I've been using my Outlook without any problems until today. I cannot sue Outlook any more and I've got the  following message:

There is a problem with the proxy server's security certificate.The name of the security certificate is invalid or does not match the name of the target site outlook.office356.com. Outlook is unable to connect to the proxy server. (Error Code 0)

I think that the issue is only in my PC as my online Outlook App is working fine.

I'd appreciate any advice on how I can fix this.

Thanks,

Milena