This field describes the ID generation algorithm recognized by Nmap, showing a possible vulnerability (to TCP Idle scan, for instance) in the system. However, many systems use a different IP ID for each host they communicate with. In this case, they may appear vulnerable while in fact being secure against the attacks.
Have a look at the scan results of the Intense scan. If you look carefully, the Nmap log shows many more then expected. Notice the port scan, showing four open ports, two of which have been diagnosed with version numbers.
Also, notice the warning line saying the OS scan results may not be reliable because Nmap was not capable of finding at least one open and one closed port.
If a message like this shows up, ...