Does the problem appear if you use do not use simpleslides? If not, does it appear if you use style=default? This will help narrowing down the cause.

I've tried a "Hello world" file and also a non-simpleslides presentation tex file, all of them work. So it seems it's simpleslides and yeah, you where right, it's the styles. I'm using "Split" for my presentation and as for the minimal I've provided BigNumber, both fail at some point. Using style=default, does not have this problem with qpdf. I'm still trying out different styles and different slide content ... Adam