Could not apply the stored configuration for monitors

Hello everyone.

After all i gotta say that I’m running Trisquel Belenos 7.0, kernel 3.13, x86_64 on a VirtualBox 5.1.22.
Well folks this is the trouble.
After an update, a message appear just after the login:

“Could not apply the stored configuration for monitors
none of the selected modes were compatible with the possible modes:
Trying modes for CRTC…”

In the first attemp I tried to install the VirtualBox Guest Addition but simpply fail. This is the log message:

“/opt/VboxGuestAdditions-5.1.22/src/vboxguest-5.1.22/buid_in_tmp: 67 /opt/
VBoxgGuestAdditions-5.1.22/src/vboxguest-5.1.22/build_in-.tmp: make: not found ”
And this other:

“vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong.
vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong.
vboxadd.sh: failed: modprobe vboxguest failed.”

The second attemp was to try to edit /etc/X11/xorg.conf , as this post explain it

https://trisquel.info/en/forum/monitor-resolution-complete-beginner

but doesn’t work and actually get the things worse becase the GUI session stop working.

The xdrandr show this message

“Failed to get size of gamma for output default
Screen 0: mínimum 640 x 480, current 640 x 480, máximum 640 x 480
Default connected primary 640x480+0+0 0mm x 0mm
640x480 73.0* “

Any suggestion?