Since the Screen Sharing feature seems to be the only one unable to connect, the best way to diagnose its behavior is by using the application directly.
Please, launch screen sharing located in:
/System/Library/CoreServices/ScreenSharing.app
The application has no visible "UI" so don't expect a fancy Cocoa interface. Instead, once you have loaded it, all you'll see is this "poor" icon in the Dock:
Click on it and then go to Preferences in the Mac menu bar. You should be presented with:
Notice the second option to only encrypt passwords and keystrokes. That's fine, but as you can see, there's no option to skip encryption altogether. Some VNC versions have incompatibilities with encryption, but this would be rather shocking since you're talking about OS X vs OS X.
In any case, once you have the settings like that, try connecting, again, in the menu bar: Connection -> New (or ⌘cmd + N).
A simple dialog appears asking you to enter the Host's name. Following your screenshots, try: 192.168.1.99 and hit enter.
We'll see what happens from here. Also, have the Console.app open on both computers, to see if there are any System messages going on (or anything related).
After half a year and 2 bounties, no-one genuine solution, so the answer appears to be a simple "You can't do that".
Best Answer
There is a very cool command line utility called
cscreen. The developer has a number of versions available. Depending on how old your Mac is, you either want the PPC version, or the Intel version. If your Mac is newer than a 2006 model, you probably want the Intel version.Once you have downloaded the disk image, double click the image to mount it, then copy the cscreen file to anywhere except the disk image. Now open Terminal. (You can search for it in Spotlight.) Once Terminal is open, you can run
cscreenby navigating to it, then typing./cscreen. For example, if you copied cscreen to your Desktop, you would navigate to the Desktop in Terminal by typingcd ~/Desktop. Once there, you would type./cscreen.To change the resolution, we first need to know what resolutions are possible. To find out, we can type
./cscreen -v. This should output something like this:Now we can choose a resolution. Assuming you want 32 bit colour depth, you can change to the resolution of your choice by typing
cscreen -i <DisplayID> -d 32 -x <width> -y <height>,and replacing the parts enclosed in <> with the actual values. I haven't tested this with a headless system over VNC, so your milage may vary. The command line option
-i <DisplayID>is optional, so if your VNC doesn't register a display ID you may still be able to change the resolution if you omit that part of the command.