FATAL: Can't read module /lib/modules/18.104.22.168-0.1-pae/kernel/drivers/net/wireless/b43/b43.ko: Cannot allocate memory
At first, I thought it was a symptom of building a kernel on a low memory machine, but I upped the swap space and tried again, only to get stuck in the exact same spot. It turns out the error is easily fixed by turning off the debug option in the /usr/src/linux/.config file. You can do this either with a text editor or "make xconfig" (or "make menuconfig", etc).
You want to replace the line:
#CONFIG_DEBUG_KERNEL is not set
It is near the end of .config.
In the configuration programs, the option to turn off is "Kernel hacking | Kernel debugging".