On newer Linux kernel versions, the interface names are different and fwbuilder doesn't match correctly. I have an ethernet interface called p33p1 and I tried to create a vlan interface under it. fwbuilder insisted that the vlan interface should be based on p33. Fortunately, I discovered the preference to disable interface name checking so I was able to continue.
It took me a while to figure out why it was matching at all, but then I realized it doesn't match the entire name. I'm not sure what the full range of possible interface names is, but maybe just match any combination of letters and numbers.