Here are the errors in the install log (hostname edited but is correct in the error log). Ring any bells for anyone? I've checked as many ways as I can think to and the FQDN comes up as valid.
<event date="Mar 14 15:58:02 +00:00" severity="2" hostName="XXXXXXXX" source="Symantec.Installation.UI.NSApplicationIdentityView.ValidateSslCert" module="SymantecInstallationManager.exe" process="SymantecInstallationManager" pid="1580" thread="1" tickCount="42375484"><![CDATA[Unable to validate fully qualified web domain name is current server]]></event>
<event date="Mar 14 15:58:02 +00:00" severity="1" hostName="XXXXXXXX" source="Symantec.Installation.UI.NSApplicationIdentityView+IISWebSite.checkWeb" module="SymantecInstallationManager.exe" process="SymantecInstallationManager" pid="1580" thread="1" tickCount="42375500"><![CDATA[Exception trying to access the web site