I don't know if they made it clear enough in the earlier posts in this thread, but...

When wiring category-5 network cable, it's not enough just for Pin1 to go to Pin1, Pin2 to go to Pin2, etc.

The wires are in special sets of twisted pairs. Certain pairs of the wires must be twisted with each other in order to prevent inductive noise and RF interference from killing your network connection. So you have to be sure to run genuine category 5 cable, and the wires have to be punched into the network block in the correct color-coded order, or else the run will fail (or at least be intermittent). The longer the run, the more likely this is to happen. A two-foot cable run with the wrong pattern of pairs might work fine, but extend that to 100 feet and you're scrod.

So. If all you're paying attention to is whether or not the source and destination pins come out right, but not paying attention to the actual wire pair order in the run itself, then that could possibly be the problem.

In the past, someone has posted a graphic of the correct Cat-5 pairings here on the BBS. Anyone have that link?