Guest Additions fail

Verifying archive integrity... All good.
Uncompressing VirtualBox 4.3.12 Guest Additions for Linux............
VirtualBox Guest Additions installer
Copying additional installer modules ...
Installing additional modules ...
Removing existing VirtualBox non-DKMS kernel modules ...done.
Building the VirtualBox Guest Additions kernel modules
The headers for the current running kernel were not found. If the following module compilation fails then this could be the reason.

Building the main Guest Additions module ...done.
Building the shared folder support module ...fail!
(Look at /var/log/vboxadd-install.log to find out what went wrong)
Doing non-kernel setup of the Guest Additions ...done.
Installing the Window System drivers
Warning: unknown version of the X Window System installed.  Not installing X Window System drivers.
...done.
Installing graphics libraries and desktop services components ...done.
Press Return to close this window...