i@ubuntu:~$ sudo do-release-upgrade
Checking for a new ubuntu release
Done Upgrade tool signature
Done Upgrade tool
Done downloading
extracting 'maverick.tar.gz'
authenticate 'maverick.tar.gz' against 'maverick.tar.gz.gpg'
tar: Removing leading `/' from member names

Reading cache

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Building data structures... Done
Reading package lists... Done
Building dependency tree
Reading state information... Done
Building data structures... Done

Updating repository information
WARNING: Failed to read mirror file

No valid mirror found

While scanning your repository information no mirror entry for the
upgrade was found. This can happen if you run a internal mirror or if
the mirror information is out of date.

Do you want to rewrite your 'sources.list' file anyway? If you choose
'Yes' here it will update all 'lucid' to 'maverick' entries.
If you select 'No' the upgrade will cancel.

Continue [yN] y
WARNING: Failed to read mirror file

Generate default sources?

After scanning your 'sources.list' no valid entry for 'lucid' was
found.

Should default entries for 'maverick' be added? If you select 'No',
the upgrade will cancel.

Continue [yN] y
Third party sources disabled

Some third party entries in your sources.list were disabled. You can
re-enable them after the upgrade with the 'software-properties' tool
or your package manager.

92% [Working]
Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Building data structures... Done

Calculating the changes

Calculating the changes

Could not calculate 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.


Restoring original system state

Aborting