Ubuntu 8.04 LTS upgrade from 7.10 fails

[Robert Stockdale IV]

I have Ubuntu Studio 7.10 installed on my workstation. When I go to upgrade
to 8.04 LTS I get the error message:

Could not calculate the upgrade

A unresolvable problem occurred while calculating the upgrade.

 This can be caused by:
 * Upgrading to a pre-release version of Ubuntu
 * Running the current pre-release version of Ubuntu
 * Unofficial software packages not provided by Ubuntu

If none of this applies, then please report this bug against the
'update-manager' package and include the files in /var/log/dist-upgrade/ in
the bugreport.

I do have ¨Unofficial software packages not provided by Ubuntu¨   however, I
don´t see how that should be an issue. If those packages don´t work after
the upgrade then I will be required to reinstall them. It should not prevent
me from using the upgrade tool to upgrade my system. It would be nice if
there was a warning about this and an option to proceed or cancel the
upgrade.
Bob
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