.arw is a camera raw file. CA will use dcraw (https://en.wikipedia.org/wiki/Dcraw) to convert that file to a TIFF, then use the TIFF to generate previews. If the TIFF is off, the previews will be off. The .arw file is stored without modification, so if you download it it will be fine.
I would suspect that dcraw is not handling your file correctly. Try running it through dcraw directly on the command line and see what you get. Assuming it's the same result as you're seeing in CA, which is likely, then make sure you're running the latest version of dcraw on your server.
