update-manager unresolvable problem 'Could not initialize the package information' (libqtcore4:i386)

[Ciaran Neeson]

I was running update-manager when my system crashed mid-way through the process. On restarting, I tried to get the update to complete but am now getting the following message from update-manager:

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Could not initialize the package information

An unresolvable problem occurred while initializing the package information.

Please report this bug against the 'update-manager' package and include the following error message:

'E:The package libqtcore4:i386 needs to be reinstalled, but I can't find an archive for it.'
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I've also tried this:
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ciaran@ubuntu:~$ sudo apt-get install libqtcore4
[sudo] password for ciaran:
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: The package libqtcore4:i386 needs to be reinstalled, but I can't find an archive for it.
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I am pretty much a complete newcomer to Ubuntu. I've tried a bunch of other processes but they all give similar error messages. Would expect update-manager to complete the last updating process, but it isn't loading up correctly any more (just giving the above-detailed error message) so I can't access it.

Release info
-----------------
ciaran@ubuntu:~$ lsb_release -rd
Description: Ubuntu 12.04.2 LTS
Release: 12.04

Package info
------------------
libqtcore4:
  Installed: 4:4.8.1-0ubuntu4.4
  Candidate: 4:4.8.1-0ubuntu4.4
  Version table:
 *** 4:4.8.1-0ubuntu4.4 0
        500 http://security.ubuntu.com/ubuntu/ precise-security/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     4:4.8.1-0ubuntu4 0
        500 http://archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

[Ciaran Neeson (ciaran-neeson)]

Eventually found a way around this - the key was:

apt-get install --reinstall libgl1-mesa-glx:amd64 libgl1-mesa-glx:i386