Hi @DavidR ,
Thanks for posting your message here, and welcome to the community forum!
If you’re using an older version of the Crossref-OJS plugin, that is likely the cause of your error. You have to be on version 3.1.2 of the Crossref XML Export plugin in order to register content automatically.
On version 3.1.1 you can still use the XML export and upload that manually, but you can’t deposit directly via the plugin.
If you have additional questions please see the PKP Community Forum or contact the Support team at PKP, the organization responsible for the Open Journal System (OJS). Because OJS is not our system, we’re very limited in how much we can help you with its use.
My best,
Isaac