Attempting to change MAC address returns "Too many open files in system"

Hello all.
I've started delving into this issue on LinuxQuestions.org, but I came here because I could really use some help specifically with Ubuntu.
I've went through most of my problem here, but I'll quickly sum it up for you guys: I had locked myself out of my own router, and thought a quick MAC spoof would let me in. Ubuntu wouldn't allow it, but Kali did and I was able to re-add myself to the whitelist. But I'm still curious about why Ubuntu wouldn't let me change the MAC, even in single user mode. Kali is based on Debian, so it isn't that much different under the hood, so why will Ubuntu not permit the change? And how can you change the MAC under Ubuntu?
Thanks in advance.