Unsolvable Screen Sharing Authentication Error

Question

Here's my scenario...
I have three Core2Duo iMacs (Let's call them "A" "B" and "C") on a local appletalk network all communicating fine in all directions via an Airport Extreme base station.
When it comes to logging into each machine via file sharing, I have no trouble accessing any machine from any other machine.
HOWEVER,
When I attempt screen sharing over the network, this is my result.
Computer "A" can access the screens of "B" and "C",
Computer "B" can access the screens of "A" and "C",
Computer "C" can access the screen of "B" but not "A"
When I attempt to log into Screen sharing from "C" to "A", I get the following error message:
*+Authentication failed to "NameofComputer"+*
*+Please verify you have entered the correct name and password.+*
I have turned screen sharing on/off, restarted, etc, but it doesn't fix that one issue.
Now, to add to the strangeness, when I access computer "A" via computer "B" through file sharing, I can see all of my drives, including an externally connected hard drive that I use for storage.
BUT, when I connect from "C" to "A" via file sharing, all of my user areas and native partitions show up, but the External drive does NOT.
Does anyone have any suggestions other than archiving and reinstalling Leopard? AND, any idea which system even has the problem? The authentication error responds so quickly that I somewhat think that authentication is not even being attempted from "C" to "A".
Any help is REALLY appreciated!
Thanks,
Chris

Answer 1

Here's just a bit more info. I created a new user on the computer that I noted as "C" and under the new user area I was able to connect to computer "A"; however, when I switch back to the original user, it still will not connect, so now I know that the problem lies somewhere in "C".
I deleted my screen sharing prefs, but that made no change.
I have verified that the sharing and network settings are consistent across all three machines.
Could there be another preference file I should attempt to delete to see if I have a corrupted preference?
Thanks again,
Chris