Custom background issue-changes not saved

Hello Everyone
I am using wordpress 4.1.1
I have developed my theme and loaded in the local server using wamp and apache in my pc.
the theme works fine, i have also the live version but i am working locally
I am learning the add_theme_support features and this morning i added the feature in my site specific plugin. THe custom background menu showed regulary in the admin panel, i can select a new image, see it in preview..everything looks working fine but onece i save, the situation comes back to the previous one and the new background image is not saved.
Same thing with the colour of the background
is there anything else i missed to do?
any tips welcome
p.s the same if i past the script in functions.php
thanks
P.