I have given up on the sandisk cruzer, One 8 GB went read only, and a 16GB which would not work in any of my Pineapples, whether it was powered by computer,battery or adapter, but it works in the laptop. I have started using the small Kingston 16 sticks, they are only slightly larger than the cruzer fit.
I had the same with a 8GB cruzer fit as well. It was less than a week old. When it goes into write protect mode, it seems to be stuck. I have tried all partitioning/format tools in both windows/linux to repartition the flash drive and none seem to work. Looking at the forums on the SANDISK website, there lots of threads complaining about the problem but no solutions. It is not just confined to the cruzer fit range. I will be trying to get a replacement SanDisk Forum BigScrote