That should do it unless you are getting some other kind of error prior to that.

The problem occurs when a print of a document crashes out for other reasons in which case those entries in the registry are left behind and then subsequently you will get that message.

Is this a Windows 10 computer by any chance?

Yes it's windows 10. I have looked in the registry and there are no jobs left behind however.

Look at KB19838 and try the steps under 'Additional Information'

We tried that yesterday, still having this issue, it made no difference.

Here is one more thing to try that has helped me with Windows 10, but I can't claim to have used it for this specific circumstance. No guarantees, but you never know.

Use regedit to go to hkey_current_config
Right click on Software and select permissions.
Add a security group for Everyone and give it full control and read permissions.

One other suggestion.
Uninstall the workstation. When prompted tell it to remove all registry entries. Go to devices and printers and remove the Sage 100 PDF converter.
Then reinstall the workstation.