WP simpleviewer gallery: doesn't center correctly when set to width 100%
 

I have a fluid width for my website: 100%, 800px minimum, 1000px maximum.
On my homepage www.bartvandermark.nl I have a slider set to width 100% and that works fine: the slider shrinks when the width of my website is between 800 and 1000 px.

I have a few WP Simpleviewer galleries and they give problems in my atahualpa theme. I want to set the width of these galleries to 100%. This is what happens with the width set to 100%:

http://www.bartvandermark.nl/portfolio/natuur/ (width set to 100%)

The gallery goes to the right, out of the body of my site

To make it better I fixed the width to 970px, in that case it looks nice but the gallery is not flexible in width so I want 100% width. How can I fix this?

http://www.bartvandermark.nl/portfolio/bruiloften/ (width set to 970px)

When I temporarily change my theme to twenty eleven the gallery is centered just fine. This gives me the impression that some setting in Atahualpa is causing this... I have no idea how to fix this. Can you give me some directions what to change?

I changed to a non-flash gallery and now it works fine :)