I did the first update in sequence and it went fine but when I tried to update to the next version it would not recognize the file, I tried both the zipped and unzipped file. I tried just putting it in the root directory of the pc and Nada, but it will see the recent update for another camera. I have updated cameras before an not had this issue .
I'd guess that you haven't actually unzipped (ie extracted) the zip file that you downloaded, and are just seeing Windows supposed-to-be-helpful view of the zip file contents.
My Camera is a European model which is why I got the firmware from their European FTP site. I was able to get it up to version 5.4.3 but was rather difficult. I had to eliminate all the other cameras off the network, go to the camera set it to defaults. shutdown the camera and the computer, reboot. reset the clock and reboot the camera, than go into and do the firmware update