before we try that can you look for a folder where your 6.4 ACR software is which contains files with a .dcp extension. In that folder is there an x100 file? If not I have extracted one from latest ACR download for mac and will need to send it to you to put in that folder. This may be wishful thinking on my part but without that file it ain't going to work in 6.4.
If you have some unzip software you may be able to extract the file yourself. Its buried several layers into that 6.4.1 downlaod file. I use 7-zip on windows. I don't know on a MAC.
If you can't do it PM me your email and I'll send it.
filename you are looking for is:
Fujifilm FinePix X100 Adobe Standard.dcp