background image "failed to load the given URL"

I have made no intentional changes to my CSS. Suddenly my background has gone gray. (And white in the header.) Same result in Firefox, Chrome, IE. Everything else about the site seems normal, including other images. I can see that the image file that is to be used for the background is in the same file location as ever and is not corrupted.
Firebug pop-up tells me “failed to load the given URL” for:
url("img/bg.gif")
The only strange thing I have noticed is that in the Dashboard editor, style.css says:
background: url('img/bg.gif') #b3b3a8;
and

#header {
	border: 5px solid #108a10;
	background: url('img/bg.gif');

Whereas when I look at style.css in Firebug I see:
background: url("img/bg.gif") repeat scroll 0 0 #b3b3a8;
and
‘#header {
background: url(“img/bg.gif”) repeat scroll 0 0 rgba(0, 0, 0, 0);`

I’m not sure if there is any significance to repeat scroll . . .

site: https://www.greenerhouse.co.za

Thank you in advance.

Please be aware when replying that I am not an expert and may need detailed instructions.