Problem conecting and file-sharing between two net-worked macs

Question

I have a Mac Pro (in an out-building in my back-garden) and an Imac (in the house) connected by a long ethernet cable (must be at least 20 metres).
I used to have no trouble connecting one to the other till recently. I still usually have no trouble connecting to the Internet from the Mac Pro using the Imac's internet connection (wireless). The problem is in clicking on the Imac connection to open it in order to share files (also using "connect to server" in Go menu).
Much of the time (but not absolutely always), it refuses to connect, and I get a "failed connection message" (or something like "server does not exist" if using other method).
Sometimes, I can connect successfully, not just as a guest but after entering admin password, and then short time later the connection will disappear. When this happens, the Imac icon previously visible in the finder window also disappears. Unplugging and replugging the ethernet cable has no effect. Once I was using Itunes shared library to play a song on the Imac, and the song just suddenly disappeared.
Just now, after the Mac Pro-to-Imac conection failed again, I substituted my Ibook for the Imac in the house, and there was no problem at all connecting both ways between it and the Mac Pro. I then reconnected the Imac to the Mac Pro and it too connected fine. This proved at least that the ethernet cable was not at fault, but no doubt the problem will re-occur.
I have tried experimenting with the Firewall settings on the Imac, e.g. to "allow all incoming connections" or to "set access for specific services"( the latter is my usual setting on the Imac), but it made no difference. Also, the Ibook has no trouble at all connecting to the Imac when the Imac firewall is set to "specific services" so why should the Mac Pro have a problem (I admit I am a little uncertain about the best setting for the Firewall, but believe "specific services" to be correct).
File-sharing options in system prefs on the Imac are clearly properly set-up or there would never be any connection at all.
Often, although the Mac Pro to Imac connection will not work, the Imac to Mac Pro will, although not today, when the Mac Pro icon similarly was not present on the Imac.
As stated, I am pretty sure that all the time the internet connection from Mac Pro to Imac still works (Mac Pro shares Imac conection).
None of this appears to make much sense and am wondering if anyone has advice.

Answer 1

Hi,
It might be me but I don't think I have fully understood the "My Name's iMac" bit.
If you mean (my Name) iMac as opposed to (My Name) iBook or Shed computer then that is a separate issue I will describe below
Does the "My Name" bit mean like mine does in this pic ?
As you can see I have used the Edit Button to change the Name of this G4 to RalphG4
In System Preferences > Network > (Connection method) > Advanced Button > WINS tab I see this on my G4
I have in fact used the same "Computer name" here (As in RalphG4)
My MacBook Pro has had the Netbois Name changed to Macbook Pro
It shows in the G4 Shares as that.
The Finder's Preferences are set to Display the Bonjour and SMB shares that I can see as I have a Mixed PC and Mac Network here
(Currently only the MacBook Pro is On as well)
SMB Shares are not on in the MacBook Pro settings so it shows as a Mac Server (Highlight and do a Get Info)
Two Computers with Same Name
In Bonjour when two computers end up with the same name (As my two did originally) these double name issue cannot be resolved and the computer may be "Seen" briefly before it then disappears
I have not tried it with SMB shares on my two Macs having had issues with Bonjour.
(Note: iChat goes one step further.
Even if the computer names are different iChat uses the Name in the My Card spot in the Address Book to show as the Buddy Name in the Bonjour Buddy List.
It cannot resolve this if both computers are logged in as the same Person.)
Another reason why a computer may show up twice is how it or they are connected.
Lets say that all are connected to a router either by Wifi or Ethernet.
They will be then seen once.
If one computer is connected by Ethernet and Wifi at the same time then it will be shown twice as each appearance is linked to the Media Access Card it is using and the IP it uses for each connection.
This can also happen if one is linked directly to another with an Ethernet connection or Wifi whilst doing the other to the router.
Back to the naming thing again.
It is better to use the Edit Button (Arrowed in Blue above) (.Local Name) rather than trying to change the computer's Name (Ralph Johns's Computer) as this is less reliable in later versions of the OS.
8:52 PM Sunday; August 29, 2010