adding a different background for a post or page

I am using a theme template and have a feeling the code of this template is blocking me from adding a new background for a new page or post.

I have used the ‘custom post background’ plugin but it doesnt work for me.
When I try to create a new background (using the plugin), it does not add a new background but instead shows no image at all.
Some other features of the plugin work but its not allowing me to have multiple backgrounds.

I have a feeling that code within my theme ‘style.css’ file is blocking me from having multiple backgrounds within my blog

Can anyone please help me with this?

I can post my style.css here if you require it

Many thanks, sound4site