how to disable backgropund picture

[Jordi Castells <jorcas writeme com>]

hi all,

I am trying to disable the background picture

I start gnome control centre, I select background options, de-select the
checkbox 'use picture as background', the example changes to a
horizontal gradient

but when I press ok (apply) button nothing hapens, the background
continues the same and the background options dialog do not closes (I
must press close button)

any idea that helps me? could be an instalation problem, how I check my
instalation?