SBG3300n can't add a WAN interface

I'm trying to pre-configure a SBG3300n to send to someone to replace a faulty one. It's not letting me add a WAN interface whatever I try. I always get: "Configure WAN Setting failed, please try again." Also, the ISP requires VLAN on the WAN interface but that option is greyed out. What might I be doing wrong? Firmware is V1.01(AADY.9) which I believe is the latest for this device.