$ sudo do-release-upgrade -d
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

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. 

[100%] 1265kB/s 0s 
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
Reading package lists... Done    
Building dependency tree          
Reading state information... Done
Building data structures... Done