audience-es755-fw.bin not found

I’m trying to compile the TX1 kernel on my Ubuntu 16.04 box, and I always get the error

MK_FW   firmware/audience/es755/audience-es755-fw.bin.gen.S
make[2]: *** No rule to make target 'firmware/audience/es755/audience-es755-fw.bin', needed by 'firmware/audience/es755/audience-es755-fw.bin.gen.o'.  Stop.

Now, I routinely build the kernel on an old Debian box. It is the same identical source tree and I configure it in the same identical way:

export TEGRA_KERNEL_OUT=kernel_out
make O=$TEGRA_KERNEL_OUT tegra21_defconfig

In the Debian machine it works a charm. I have spent a couple hours trying to figure out what is wrong with my new setup with no avail.
The compiler is the GCC 4.8.5 provided in the R28.1 download page by Nvidia (re-downloaded just 10 minutes ago)
Any ideas? Thanks!

I have that file in a download. You say it is the same tree, but are you positive? Were they both created with a command? Have you done an in-tree build, mrproper, or clean ever, at any time? In the parent directory full path are there spaces or odd characters in the path name in the one which fails?