I just upgraded mine. Same problem with the 121MB file, but there is another (not particularly complicated) way to do it
Grab the iriverStoryEB05.z01 to iriverStoryEB05.05 and the iriverStoryEB05.zip file. If you have a multipart-able unziper, unzip the zip file. If you are using Linux and don't have a multipart-able unziper (which was my case), open a terminal in the directory where you saved the files and enter :
cat iriverStoryEB05.z01 iriverStoryEB05.z02 iriverStoryEB05.z03 iriverStoryEB05.z04 iriverStoryEB05.z05 iriverStoryEB05.zip > iriverStory115.zip
then unzip iriverStory115.zip. You will now have a file called iriverStoryEB05.HEX
copy it to the root directory of your Cover Story, cleanly eject the device, unplug it. It should find the update, check it and then start the actual update. Takes a couple of minutes, then it reboots et voilą!
No idea whether it was worth it yet of course, but well ...