There can be an exception from apt at several times. Unfortunately APT only shows a translated error message and no codes. Often it is unclear what the user should do.
Furthermore there can be a broken system, e.g. delted /var/lib/dpkg/updates (bug 791715) or failing to open TagSection
E:Encountered a section with no Package: header, E:Problem with MergeList /var/lib/apt/lists/br.archive.ubuntu.com_ubuntu_dists_maverick_universe_binary-i386_Packages, E:The package lists or status file could not be parsed or opened.
<https://wiki.ubuntu.com/SoftwarePackageOperations#general>: "If a file needed by apt is missing or unparseable, the alert should have primary text “Software can’t be installed or removed because an essential file is unreadable.”, and secondary text “No changes were made. To fix the problem, restore the file from backup, or reinstall Ubuntu.”"
E:Write error - write (28: No space left on device), E:Can't mmap an empty file, E:The package lists or status file could not be parsed or opened.
<https://wiki.ubuntu.com/SoftwarePackageOperations#general>: "If there is not enough disk space, the primary text should be “Software can’t be installed or removed because there is not enough disk space.”, and secondary text “No changes were made. Deleting other unwanted files may free up enough disk space.”"
E: The package google-chrome-stable needs to be reinstalled, but I can't find an archive for it.
E:Type 'http://ppa.launchpad.net/pdfmod-team/ppa/ubuntu' is not known on line 2 in source list /etc/apt/sources.list.d/pdfmod-team-ppa-maverick.list
<https://wiki.ubuntu.com/SoftwarePackageOperations#general>: "For any other error, the primary text should be “Software can’t be installed or removed because of an unknown error. Sorry about that.” and secondary text “No changes were made.”."
SystemError: E:The package index files are corrupted. No Filename: field for package ubufox.
<https://wiki.ubuntu.com/SoftwarePackageOperations#general>: "If a file needed by apt is missing or unparseable, the alert should have primary text “Software can’t be installed or removed because an essential file is unreadable.”, and secondary text “No changes were made. To fix the problem, restore the file from backup, or reinstall Ubuntu.”"
So does this need fixing in apt, not just aptdaemon? If apt returned an error code, not just a translated error message, the aptdaemon GUI could offer ways of recovering from the error. For example, the "No space left on device" error might trigger an apt-get autoremove. The "The package lists or status file could not be parsed or opened" error (why isn't that two separate errors?) might trigger regenerating the package list or restoring it from backup. And so on.