I use RawTherapee or UFRaw (mostly the second one).
Check, whether in RAW parameters you have set DNG format and DNG file extension. DNG is universal filetype for raw images, so you'll be able to use almost any software.
CHDK "raw" (saved as CR2 or CRW or others non-DNG) are not any "real" filetypes. These files are jus sensor dumps. That's why there's not a lot of programs, that handle them... So usage of DNG is better idea;)