Thank you for taking the time to report this bug and helping to make Ubuntu better.
I think the problem comes from the uninstall that left the system in an unstable state, rather than the reinstall.
Can you try purging nagios2 completely (sudo apt-get purge nagios2-common nagios2), then reinstall nagios2 ?
Do you remember what the original uninstall error was ?
Thank you for taking the time to report this bug and helping to make Ubuntu better.
I think the problem comes from the uninstall that left the system in an unstable state, rather than the reinstall.
Can you try purging nagios2 completely (sudo apt-get purge nagios2-common nagios2), then reinstall nagios2 ?
Do you remember what the original uninstall error was ?