Azure AD Connect – Unable to validate credentials due to an unexpected error.
In case you will get the following error message at connecting to Azure AD, there will be a good chance that only the password for your Azure AD global administrator is expired.
So try to login Azure AD Connect by using the interactive authentication. Therefore change to the directory where Azure AD Connect binary is homed.
C:\Program Files\Microsoft Azure Active Directory Connect
Start Azure AD Connect by using the /InteractiveAuth switch.
Here you can see that only the password from my Azure AD global administrator is expired and I have to set a new one.
After that I was able to connect to Azure AD.
If this wasn’t your issue, please read the article from Microsoft below about troubleshooting Azure AD connectivity.
Troubleshoot Azure AD connectivity