adding ssd

Hey Guys'n Girls, I added a second NVME SSD on my intel NUC. Boot Media is a SATAIII SSD. After adding that NVME SSD the WebUI is not reachable anymore. I just managed to troubleshoot stuff like adding PCI devices, that changes their ID. The network adapters seem to be ok. When I do a "ip addr...

I just created a Proxmox 5.1 box on a 250 GB SSD. Have not created VM yet. I want to add a second SSD this ine is a samsung EVO 860 500GB. it is listed in DISKS. When I try to initialize it as GPT I get an error 3. Am I doing this wrong? Thanks in advance.