Mac to Mac

[HarmanyHank]

I have two iMacs - iMacA and iMacB - which are both running the same version of Snow Leopard and are both on the same home network, with identical sharing options turned on. iMacA is a 2011 vintage and iMacB is a mid-2007 vintage. Both computers are connected via ethernet to an Apple Airport Extreme router and both also have wi-fi turned on.

When both machines are turned on, iMacA can see iMacB in the Finder under the Devices heading and can access the Public File of iMacB as well as other shared files (after entering the correct Userid and password).

On the other hand, iMacB can see iMacA in the Finder under the devices heading BUT cannot access either the Public file of iMacA nor any other files. After the few seconds of searching, I always get the cannot connect message.

One other relevant piece of information is that iMacB (the one with the problem) CAN connect (via wi-fi) to a MacBook Air (running Mountain Lion) which we have on the same network.

I'm wondering if anyone has any suggestions as to what this connection problem with iMacB might be or what things I might try to troubleshoot it.

Thank you.