Why is Mac-to-Mac screen sharing just hanging?

I have my iMac set up with:

• Firewall off
• Screen sharing on for specific user, no general VNC password
• File sharing on (with liberal access)

I want to connect to it's screen from my MBPro. Whenever I try to start a screen sharing session from the MBPro to the iMac, either via Finder's screen sharing dialog or by calling the Screen Sharing app directly, it just hangs. And hangs. And hangs. And eventually the "Connecting..." window just quietly disappears and no screen is shared.

I checked Keychain to make sure there isn't a bad password set for the iMac and, nope, nothing there. I'm not being prompted for a user name or password from Screen Sharing when it runs.

I don't have a central user authority on my network. Each Mac has its own local user settings. But the user names and passwords are identical.

I can connect successfully using Jolly's Fast VNC. It actually finds the iMac via Bounjour broadcast. But this software, technically, is not free and I'm perplexed as to why the built-in Mac approach isn't working for me.

Update: here are the screen sharing settings on the iMac.

And this is what I have set when you click on the 'Computer Settings...' button:

Jolly's Fast VNC continues to find (via Bonjour) and connect to this machine without any issues. I have to give it my user name and password for the iMac when I want to connect. Finder, on the MBPro, can connect to the file shares (using my iMac user name and password) just fine. Clicking 'Share Screen' in the Finder window wakes up the iMac -- the display turns on and what not. But the connect times out.

Are there log files for Screen Sharing on the MBPro I can look at to debug this? What about log files on the iMac for Screen Sharing? Something that might shed some light on why Screen Sharing says it's connecting and then just mysteriously stops?

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).

since your a site to site mac network, your networks dns servers need to be update with A records of your mac machine names, to whatever.whaterver.com or .edu or what ever you are,

that way the dns can resolve host names to ip addresses, it is especially complex on spaced names, windows machines with simple names are easy to convert, name to ip either via WINS or DNS, so you have 2 choices for the future,

1: create local name mappings to STATIC ip addresses on the macs into your /etc/hosts file on EACH mac

2: buy your it folks some donuts and coffee and kindly ask them to setup some a records in DNS for your macs.

3: if you have an Xserv it should do this for you, just make sure your directory utility is setup to use it.

hope that helps.