[  449.307668] [ERROR]Cannot access secondary GPU - error: Could not load GPU driver

[  449.307808] [ERROR]Aborting because fallback start is disabled.

...
Sep  2 18:29:02 fondation bumblebeed[835]: modprobe: FATAL: Module bbswitch not found.
Sep  2 18:29:02 fondation bumblebeed[835]: [   11.652807] [ERROR]Module bbswitch could not be loaded (timeout?)
Sep  2 18:29:02 fondation bumblebeed[835]: [   11.652818] [WARN]No switching method available. The dedicated card will always be on.
Sep  2 18:29:02 fondation bumblebeed[835]: [   11.653932] [INFO]/usr/sbin/bumblebeed 3.2.1 started
Sep  2 18:36:16 fondation bumblebeed[835]: [  449.307558] [ERROR]Module nvidia could not be loaded (timeout?)
Sep  2 18:36:16 fondation bumblebeed[835]: [  449.307599] [ERROR]Could not load GPU driver

mkdir -p '/usr/src/bbswitch-0.8'
cp Makefile bbswitch.c '/usr/src/bbswitch-0.8'
sed 's/#MODULE_VERSION#/0.8/' dkms/dkms.conf > '/usr/src/bbswitch-0.8/dkms.conf'
dkms build -m bbswitch -v 0.8
Error! Your kernel headers for kernel 4.1.0-rc3-wl-ath+ cannot be found.
Please install the linux-headers-4.1.0-rc3-wl-ath+ package,
or use the --kernelsourcedir option to tell DKMS where it's located
Makefile.dkms:16: recipe for target 'build' failed
make: *** [build] Error 1