Hi Grant,
I am the person referred to in the first post.
My email is in my profile and some people use it contact me.
I am running Mavericks at my end and Rod and I have been text chatting and Screen Sharing in iChat/Mavericks.
As you know later versions of the OS come with the Apple Remote Desktop client end installed along with the OS.
This "engine" works for Apple Remote Desktop, the Finder Screen Sharing option (Finder > Go Menu > Go to Server > VNC://xxx.xxx.xx.x) and the iChat (or higher) Screen Sharing.
Rod has three computers that he is using to Screen Share using the alternative Network Window > "server" Highlight and then the Screen Share Button which invokes the Screen Sharing app.
I could share my Mavericks/iMac screen with Rod but I was only seeing a white screen from Rod's Macbook.
As it was in iChat/Messages we could still talk to each other.
I could actually Screen Share in iChat/Messages to Rod and VNC:// share to my Snow Leopard computer at the same time and show Rod the Desktop and Browser on the Snow Leopard computer.
We spent some time on Saturday on this and again on Sunday which was Text Chatting and sending pics.
At present Rod is not trying to use the app over the internet (which would require Port Forwarding or the Airport's equivelant).
He is just trying to get all three computers doing the same thing in both directions.
I am using Little Snitch at my end and from the Alerts I get I can tell Rod's Modem is not routing and the Airport devices is the one doing the Login to the ISP. (iChat/Messages shows the Public IP and the LAN IP in Error Messages as well)
During the Screen Sharing we did on Saturday I did also see his Airport's settings.
In his Macbook's Firewall he is showing that the Screen Sharing (pulled from the System Preferences > Sharing Pane) is allowed via the items above the line in the list in the Firewall.
However further down the list is the screensharingd, the daemon that deals with this. At times it is showing that it is turned Off, despite specifically changing it.
Rod is also looking in the System Profiler and seeing the items listed in the Firewall and the Firewall can report it "On" but the list reports it as Blocked.
We did not try a Screen Share of his screen with the Firewall Off.
My feeling is that .plist somewhere that contains the info for the Firewall settings is no longer Writable by Rod.
I can't seem to find the responsible item on my computer to suggest if Rod removes it on his end or checks that he has Ownership and Read and Write Permission.
We started by discussing using the Combo version of the last update he did to possible provide a "correction" that it can do in some cases.
We then also talked about doing a reinstall as a way of shortening the process and realistically a cleaner way of doing things.
Of course the other possible is that the actual Apple Remote Desktop engine is the item with a flaw and that an reinstall would be the way to go anyway.
It was while we were texting on Sunday that Rod download the reinstaller item on his iMac when he would need it on his Macbook.
It was at this point that I went Off line my time yesterday.
9:49 pm Monday; November 18, 2013
iMac 2.5Ghz 5i 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad