[Koha] Problems trying to upgrade from Koha 17.11

Hi, I am currently running Koha 17.11 on Ubuntu server 16.04 on Mysql 5.7. I'm wanting to upgrade Koha but am having problems with the "sudo apt- get install koha-common" step. I'm getting the following error: koha-common : Depends: libnet-oauth2-authorizationserver-perl but it is not going to be installed On googling I have seen a lot of discussion of this issue but have not been able to find a definite solution. I found a few suggestions but none of them worked. Can anyone point me in the right direction to find a solution for this? Thanks for any help you can give me. Regards, Tim Auld Webmaster Northern Philatelic Library Minneapolis, Minnesota.