Homegroup missing some files

[jccurd]

I finally upgraded my faithful old XP desktop to shiny new Dell XPS Windows 7 64-bit desktop. We also have two Windows 7 64-bit laptops. We both take lots of photos, most often Canon RAW .CR2 files, so I set up a Homegroup intending to make all photos available between all machines. Great idea!

Now, between my desktop and my laptop (both Dell machines, though probably irrelevant), I can see everything I want to see. However, when those two machines look at the third machine (Sony VAIO laptop), they "see" only its .JPG files, not its .CR2 files. I tracked the problem down to there being no permissions granted to "HomeUsers" on that Sony laptop for any of its .CR2 files. It DOES have permission granted for HomeUsers where its .JPG files are concerned. I manually added the HomeUsers permission on one .CR2 file and, lo and behold, it became visible to the other machines.

What I can't figure out is why the "HomeUsers" don't get permissions granted, but just for .CR2 files, on that machine when it joins the Homegroup. Any ideas, please, anyone?