AFP File Sharing not Working
Disable IPv6 and WiFi.  Plug both in via Ethernet.  Verify your targets IP.  Turn AFP and all other sharing settings off on the target, and wait for it to disappear from the sidebar on the machine you're connecting from.  Then re-enable AFP sharing on the target, and see it come back on the source.

Ping the IP, or even the name (foo.local if the computer's name is foo).  Try connecting by clicking on it from the sidebar - failing that try using the Go menu (connect to server) and putting in a URL in the format afp://&lt;name or IP here&gt;.

Let us know how it goes.

EDIT: then, once that works properly, change one thing at a time.  Enable WiFi on one machine and remove the ethernet cable.  Then test.  Then do the same on the other machin, and test.  Then enable IPv6 on one.. test.  Then the other.  Etc, until you've worked your way back to how you want your machines to be set up.  This can also help us isolate where the problem is happening (if you re-enable WiFi and sharing stops working...)