Typically, I update all my Kindle devices manually as I prefer not to sync with Amazon.  For the first time ever, I cannot update a Kindle.  I have downloaded the appropriate .bin file, transferred it to the 
root directory and ejected the device.  Oddly, the "Update Your Kindle" remains greyed out and when I reconnect and check the contents of the root directory the .bin file has vanished.
I have successfully transferred the file three times and each time it apparently disappears when I eject the PW.  Prior to transferring, free space is 665MB, and after 466MB, further confirmation that the file has transferred.
I am baffled.  Any ideas?