OK, so this is better, but now I get:
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/main/binary-i386/ InRelease Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/restricted/binary-i386/ InRelease Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise InRelease Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/main/binary-i386/ Release.gpg Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/restricted/binary-i386/ Release.gpg Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/main/binary-i386/ Release Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/restricted/binary-i386/ Release Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/main/binary-i386/ Packages/DiffIndex Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/restricted/binary-i386/ Packages/DiffIndex Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/main/binary-i386/ Translation-en_US Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/main/binary-i386/ Translation-en Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/restricted/binary-i386/ Translation-en_US Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/restricted/binary-i386/ Translation-en Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/main TranslationIndex Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/restricted TranslationIndex Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/main Translation-en_US Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/main Translation-en Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/restricted Translation-en_US Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/restricted Translation-en Ign http://security.ubuntu.com precise-security InRelease Ign http://archive.ubuntu.com precise InRelease Ign http://archive.ubuntu.com precise-updates InRelease Hit http://security.ubuntu.com precise-security Release.gpg Hit http://security.ubuntu.com precise-security Release Hit http://archive.ubuntu.com precise Release.gpg Hit http://archive.ubuntu.com precise-updates Release.gpg Hit http://security.ubuntu.com precise-security/main amd64 Packages Hit http://archive.ubuntu.com precise Release Hit http://archive.ubuntu.com precise-updates Release Hit http://archive.ubuntu.com precise/main amd64 Packages Hit http://security.ubuntu.com precise-security/restricted amd64 Packages Hit http://archive.ubuntu.com precise/restricted amd64 Packages Hit http://archive.ubuntu.com precise/main i386 Packages Hit http://security.ubuntu.com precise-security/main i386 Packages Hit http://archive.ubuntu.com precise/restricted i386 Packages Hit http://security.ubuntu.com precise-security/restricted i386 Packages Hit http://security.ubuntu.com precise-security/main TranslationIndex Hit http://security.ubuntu.com precise-security/restricted TranslationIndex Hit http://archive.ubuntu.com precise/main TranslationIndex Hit http://archive.ubuntu.com precise/restricted TranslationIndex Hit http://archive.ubuntu.com precise-updates/main amd64 Packages Hit http://archive.ubuntu.com precise-updates/restricted amd64 Packages Hit http://archive.ubuntu.com precise-updates/main i386 Packages Hit http://archive.ubuntu.com precise-updates/restricted i386 Packages Hit http://security.ubuntu.com precise-security/main Translation-en Hit http://archive.ubuntu.com precise-updates/main TranslationIndex Hit http://archive.ubuntu.com precise-updates/restricted TranslationIndex Hit http://security.ubuntu.com precise-security/restricted Translation-en Hit http://archive.ubuntu.com precise/main Translation-en Hit http://archive.ubuntu.com precise/restricted Translation-en Hit http://archive.ubuntu.com precise-updates/main Translation-en Hit http://archive.ubuntu.com precise-updates/restricted Translation-en Reading package lists... W: Duplicate sources.list entry cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315)/ precise/main i386 Packages (/var/lib/apt/lists/Ubuntu%2012.04%20LTS%20%5fPrecise%20Pangolin%5f%20-%20Alpha%20amd64%20(20120315)_dists_precise_main_binary-i386_Packages) W: Duplicate sources.list entry cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315)/ precise/restricted i386 Packages (/var/lib/apt/lists/Ubuntu%2012.04%20LTS%20%5fPrecise%20Pangolin%5f%20-%20Alpha%20amd64%20(20120315)_dists_precise_restricted_binary-i386_Packages) W: You may want to run apt-get update to correct these problems
Presumably this is because apt-cdrom isn't multiarch-aware. I've attached the sources.list that it now generates.
OK, so this is better, but now I get:
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/ main/binary- i386/ InRelease restricted/ binary- i386/ InRelease main/binary- i386/ Release.gpg restricted/ binary- i386/ Release.gpg main/binary- i386/ Release restricted/ binary- i386/ Release main/binary- i386/ Packages/DiffIndex restricted/ binary- i386/ Packages/DiffIndex main/binary- i386/ Translation-en_US main/binary- i386/ Translation-en restricted/ binary- i386/ Translation-en_US restricted/ binary- i386/ Translation-en security. ubuntu. com precise-security InRelease archive. ubuntu. com precise InRelease archive. ubuntu. com precise-updates InRelease security. ubuntu. com precise-security Release.gpg security. ubuntu. com precise-security Release archive. ubuntu. com precise Release.gpg archive. ubuntu. com precise-updates Release.gpg security. ubuntu. com precise- security/ main amd64 Packages archive. ubuntu. com precise Release archive. ubuntu. com precise-updates Release archive. ubuntu. com precise/main amd64 Packages security. ubuntu. com precise- security/ restricted amd64 Packages archive. ubuntu. com precise/restricted amd64 Packages archive. ubuntu. com precise/main i386 Packages security. ubuntu. com precise- security/ main i386 Packages archive. ubuntu. com precise/restricted i386 Packages security. ubuntu. com precise- security/ restricted i386 Packages security. ubuntu. com precise- security/ main TranslationIndex security. ubuntu. com precise- security/ restricted TranslationIndex archive. ubuntu. com precise/main TranslationIndex archive. ubuntu. com precise/restricted TranslationIndex archive. ubuntu. com precise- updates/ main amd64 Packages archive. ubuntu. com precise- updates/ restricted amd64 Packages archive. ubuntu. com precise- updates/ main i386 Packages archive. ubuntu. com precise- updates/ restricted i386 Packages security. ubuntu. com precise- security/ main Translation-en archive. ubuntu. com precise- updates/ main TranslationIndex archive. ubuntu. com precise- updates/ restricted TranslationIndex security. ubuntu. com precise- security/ restricted Translation-en archive. ubuntu. com precise/main Translation-en archive. ubuntu. com precise/restricted Translation-en archive. ubuntu. com precise- updates/ main Translation-en archive. ubuntu. com precise- updates/ restricted Translation-en apt/lists/ Ubuntu% 2012.04% 20LTS%20% 5fPrecise% 20Pangolin% 5f%20-% 20Alpha% 20amd64% 20(20120315) _dists_ precise_ main_binary- i386_Packages) apt/lists/ Ubuntu% 2012.04% 20LTS%20% 5fPrecise% 20Pangolin% 5f%20-% 20Alpha% 20amd64% 20(20120315) _dists_ precise_ restricted_ binary- i386_Packages)
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise InRelease
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) dists/precise/
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/main TranslationIndex
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/restricted TranslationIndex
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/main Translation-en_US
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/main Translation-en
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/restricted Translation-en_US
Ign cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315) precise/restricted Translation-en
Ign http://
Ign http://
Ign http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Hit http://
Reading package lists...
W: Duplicate sources.list entry cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315)/ precise/main i386 Packages (/var/lib/
W: Duplicate sources.list entry cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Alpha amd64 (20120315)/ precise/restricted i386 Packages (/var/lib/
W: You may want to run apt-get update to correct these problems
Presumably this is because apt-cdrom isn't multiarch-aware. I've attached the sources.list that it now generates.