Building data structures... Done 

Calculating the changes

Calculating the changes

Could not calculate the upgrade 

An 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 using the 
command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. 


Restoring original system state

Aborting
Reading package lists... Done    
Building dependency tree          
Reading state information... Done
Building data structures... Done 
=== Command detached from window (Mon May  2 15:31:18 2016) ===
=== Command terminated with exit status 1 (Mon May  2 15:31:28 2016) ===