CF 128/256MB cards not downloading files

I work for an engine manufacturer, and we use 128/256MB CF cards in out engine control computer.  We have used SanDisk cards in our engine control computers before and they have worked fine, however, we just got some new SanDisk cards and the engine computer does not want to download the files saved on them.  I have reformatted the cards and downloaded the software onto them using different desktops/laptops.  I have also tried to use different engine control computers and the same cards do not download the information to the engine control computer.  I have used a CF card that I know works, reformatted it and loaded the same software onto it as the other cards and it still works fine. Given everything is exactly the same, why would some cards work and some not work?  Has anyone else experienced something like this?

Thanks for your help,