"can't install on disk running OS X 10.11.4" and "can only install on disk running OS X"......its been 12 hours and i haven't figured it out, got side tracked and still haven't gotten antivirus software. I'm not the brightest when it comes to computers and had no idea whatsoever to do when running the Disk Utility.
Flex
One of my colleagues has asked a moderator to move your message over to the Forum here specifically for Norton and Macs. When/If this happens and you come here you should see a link to the new location but if not this link would seem to apply to your situation.
So make sure your product is fully uptodate. If necessary one of the users in the Mac Forum will be able to tell you exactly how best to proceed especially if you have the upgraded Mac OS and don't have the latest NIS for Mac.
Product Update: Norton product support for El Capitan - OS X 10.11
In general NIS, NAV and N360 are no longer on sale but are still supported technically. However you may want to consider upgrading to the current Norton Security which comes in 3 sub-versions.
Again the users on the Mac forum here can advise you.
Flex
That's a Mac isn't it.
Googling on that version of OS-X I see some references to avoiding it ..... !
NIS is also an older version of the Norton series which is discontinued although still technically supported so it may be better for you to upgrade to the current Norton Security choosing the version best suited to your needs.
To help with advising you on this -- by others who know the subject area -- can you say whether you need protection on a mix of Windows and other systems eg Apple and Android and if so how many in all since Norton Security comes in 3 sub versions covering different numbers of devices and with some differences in secondary features.