Yes, I have tried importing the certificate and got an error like "invalid certificate format".
My code signing key+certificate was originally PKCS#12, but I have exported the certificate and private key as X509 base 64. I have tried including or not the root and intermediate CAs in the certificate file, but it makes no difference. The root CA is already in the "Trusted server CAs" of the appliance, for that matter.
Thanks a lot for answering, I will keep trying exporting the keys in other formats but not knowing exactly what the appliance expects I didn't know if I was going anywhere.
Considering the obsolescence of our appliance, I too am very aware of this and strongly recommended upgrading to the management months ago... I guess considering the ever-growing Java restrictions and the issues with Windows 10 last update, it will also be largely useless soon.