i typed in this command

dpkg-reconfigure -pmedium xserver-xfree86

i went through all the prompts and this is what i got at the very end

dexconf: cannot generate configuration file;
xserver-xfree86/config/device/identifier not set. Aborting. Reconfigure the X
server with "dpkg-reconfigure xserver-xfree86" to correct this problem.
Unable to write X server configuration file.

why is it not able to write the file?

i restarted and it is in 1024X768 (i think)but it is still is in 60 Hz refresh rate what goin on?