verify server server id

I assume you are trying to connect to the internet and during the connection a pop up a warning dialog box stating this "Safari can’t verify the identity of the website (URL)"

The first thing here is make sure your systems date & time are correct. Go into Date & Time preferences and make sure the 'Set date and time automatically" is checked and the time server is set to one of Apples servers.

You may also need to refresh your systems DHCP lease. What likely has happened here is the DNS server connection is not getting though the host (server) you are trying to connect to is one you have accessed before so the cached values are getting you there but the DNS connection failed to double check.

Heres a write up from OS X Daily that goes over some of the issues if your settings are correct as your connection could be being spoofed! Fix a “Safari Can’t Verify the Identity of the Website…” Error Message

Here's a bit more on DHCP & DNS:

• TCP/IP Dynamic Host Configuration Protocol (DHCP)
• TCP/IP Domain Name System (DNS)