If you are having trouble mounting a JFFS2 file system on a Compulab cm-x270 module, you may have a device that has a NAND flash with 16KiB eraseblocks.  All of the devices I have personally used to date have had 128KiB eraseblocks, but I just helped a cm-x270 user through some flash issues and after much pain discovered the eraseblock size was 16KiB on his module.  A variable has been added to the cm-x270.conf file in OE to set the eraseblock size that can be overridden in your local.conf file if you are using OpenEmbedded to generate jffs2 images:

http://www.openembedded.org/repo/org.openembedded.dev/conf/machine/cm-x270.conf