Check if the customer is using <a href="https://www.papercut.com/discover/integrations-and-customizations/integrations/">online payments</a>. PaperCut MF version 16.1 and below are not compatible with the current PaperCut Payment Gateway Module. The installer for PaperCut MF will generally warn you during the upgrade about any gateways. You will need to install a new version of the gateway module after you have upgraded to the current release.