just download nis 2011 i i have come across the same error that i had with build 18.1.0.37 which was posted : http://community.norton.com/t5/Norton-Internet-Security-Norton/i-can-t-install-build-18-1-0-37/td-p/273166
i emailed the logs last time as per tim instructions and have again come across the same issue on the retail version
win 7 64bit sp1
nis 2011