Very first version of 12.1, wouldn't recommend it but if you have to it threw this error:
Symantec Endpoint Protection has detected that there are pending system changes that require a reboot. Please reboot the system and rerun the installation.
MSI (c) (38:34) [12:36:34:418]: Product: Symantec Endpoint Protection -- 4Symantec Endpoint Protection has detected that there are pending system changes that require a reboot. Please reboot the system and rerun the installation.
Did you reboot?
See here steps if you've already rebooted, you need to delete a specific reg key and try again:
https://support.symantec.com/en_US/article.TECH95608.html