Screen sharing not working on MacBook

I have two MacBooks and a MacBook Pro, all three of them are connected to the same .mac account, their sharing settings are set identically, all three are running Leopard but only one of the MacBooks can view other screens using screen sharing. The other two show nothing (even though they can connect to the drives of the other machines). The only difference I can find is that the one that works hasn't had it's EFI firmware update or recent Java security update.

I just can't see how either of those would affect this issue... does anyone have any suggestions ideas or solutions?
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I would make sure you run software update on all the machines and get them up to date. Tell us how you are currently sharing and how you want to share. Is it over the internet? On a local network? I would think if you are doing it over the internet either with back to my mac you shouldnt have a problem as long as you have the settings on all machines to allow that connection (system prefs > MobileMe > Back to My Mac) the other way I see you doing it is with iChat AV, if that is what you are trying to do then you need to have two separate accounts in order to do the screen sharing. It would be like calling yourself from your cell phone if you are using the same MobileMe (.Mac) account. Make sense? Hope that clarifies.
KTMCAuthor Commented:
OK I should clarify, when I say Screen Sharing I mean the actual application 'Screen Sharing' that runs as part of Back to my Mac (iChat AV works fine, but is useless to me in this situation as my goal is to take one machine with me as a remote and be able to access the other machine's screens from that remote location, currently only one of the three is able to do that, and I want it to work for all three).

All of the machines are completely up to date except the lone MacBook that can connect via Screen Sharing successfully. The only reason I haven't updated it yet is of course because it's the only one that is actually doing this right, and all the fully updated machines are having problems.

All machines are set up correctly under the Back to my Mac panel in the Mobile Me preference pane and all of the machines are logged in to the same Mobile Me account.

It doesn't seem to matter whether I try it locally or remotely, I can still only get one of the three to work.

I should also mention that a couple of weeks ago the other two were working correctly and are suddenly not... I tried a complete re-install on the second MacBook in the hope that running the 10.5.5 combined update would fix it but alas it was not to be...
KTMCAuthor Commented:
Update, I have solved this one on my own. Turns out that the solution is to:

1. Delete all Kerberos .plist files from both computers (in the root and system libraries)
2. Open keychain and access the kerberos tickets and delete them
3. While still in keychain delete the network passwords for all computers
4. reboot

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