Could not determine the upgrade

[R Kimber]

Hi:

On trying to upgrade from 10.10 to 11.04 I get:-

Could not determine the upgrade

An unresolvable problem occurred while calculating the upgrade:
E:Error, pkgProblemResolver::Resolve generated breaks, this may be caused
by held packages.

 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 bug report.

According to Synaptic, I have no 'pinned' packages (which is what I
understand 'held packages' to mean. I'm not upgrading to a pre-release
version, and I'm not running a pre-release version.

Before reporting a bug, I have two questions:

1) Does 'Unofficial software packages' mean *any* third party
application that isn't part of the Ubuntu distribution?  That's what it
seems to mean, yet it seems so absurd that one can't upgrade a system if
you've added any unofficial application that I thought I would ask.  Before
giving me the above message, the installer disabled third party sources, so
I assumed it would be OK.  Nothing I've added is what I would regard as
part of *the system*.

2) What now? Does the error message mean that there is no upgrade path at
all, and that I have to re-install?  Or is there some work-around?
Would deleting unofficial software be the solution? If so, how do I get
a list of these?

- Richard
-- 
Richard Kimber
Political Science Resources
http://www.PoliticsResources.net/