you can install it on workgroup , try to copy the package manually and run the setup.exe
it might be cause of pending reboot
update the root certifcate
http://webcache.googleusercontent.com/search?q=cache:ssln34o3sY4J:www.symantec.com/business/support/index%3Fpage%3Dcontent%26id%3DTECH217284+&cd=1&hl=en&ct=clnk&gl=in