CAUSE:
This error is generated mostly when the back end server nodes participating in the web server farm aren’t responding to the connectivity verification from the ISA Server. When you receive this kind of error then under the Monitoring > Connectivity Verifiers, you will see that the server(s) are disconnected. This may be due to network issues or server not available.
RESOLUTION:
- Make sure that you are able to access the servers internally
- When using PING as a connectivity verifier method then make sure you are able to ping the server(s) from the ISA Server
- Try changing the connectivity verifier method from PING to HTTP URL
Cheers
Inderjeet 