A while ago, I was on a project where we were working with another division the company, and were using 3rd party GIS products to sync up our data. We were setting up a demonstration, and were on a telcon during the setup. I had no problem getting the GIS product to communicate to the master database, but the other division was having issues.
Initially, they thought that my system was interrupting theirs. So, I unplugged the network cable from my machine. Still, their problem persisted. Then it got weird.
They asked me to unplug the power of my machine. When I asked why, they said that I might have been using Ethernet over power, to which I replied that there was no way this stock cheap machine was equipped with that specialty hardware, it was just a regular old power cable. Despite this, they insisted that was the problem.
So, I did what any sane person would do, and just told them over the telcon that I had unplugged the power of the machine, instead leaving it plugged in and on, but still disconnected from the network. And of course, after I told them it was unplugged, their problem mysteriously vanished. I still don't know what the problem was. I assume that it was probably something silly and they didn't want to look foolish on the call.
