Thanks for your report.
Please revert Xorg packages from oibaf repository to official Ubuntu
versions and try the upgrade again.
I'm closing this report because it is not a bug with Ubuntu. Don't
hesitate to submit any bug you may find.
** Changed in: ubuntu-release-upgrader (Ubuntu)
Getting this error message,
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
