Sliders doesn't add (existing) posts

Dear Sir,

I have a question, regarding to your beautiful theme named NewsMag.

I have a few sliders I want to add, but when I check the box to add existing posts, it will not show them on my homepage.
I have also tried it with a new post, I annot get it to work.

It just shows the sliders empty.
Does it have something to do with the Custom Fields?

What am I doing wrong?

Regards,