Our os-deployer has not been working for several weeks. During the installation form pxe we have message like in topic that Operating System Loader has no signature. Incompatible with SecureBoot.

I tried already create new PXE media, but without success. Any ideas what can i do to resolve it. We didn't change devices BIOS settings. 

The device model does not matter. Deployed devices start downloading nbp file, but after we have this kind of message.