The information, although useful and pretty complete, contained some factual errors, I did not want to throw anyone off, in addition, I found this thread:
Which had the same problem and a few solutions that I am working to test out right now.
Something about the configuration of our host is not allowing the PDF viewer window to resolve a https request.
Thanks for touching base, I love invoice ninja, I have configured over 60 clients who now use it and most of them white label licenses.
Hopefully I can get a proper work around for this very persistent issue.
I will let you know what works for us.