I ran a line to my 3rd floor when I moved in. After kicking the phone, checking connectivity and cursing a lot I discovered that my wiring was crossed. I spent many years running wires across oil rigs, meticulously planning and documenting my wiring through multiple junctions, so of course the phone problem couldn't possibly be MY error. Doh!
Later I discovered that the intricate and old network of lines running throughout the house for about 8 ports was crossed in several places, but had just the right number of crosses to make it work. Like a fool I decided to fix it all. Took me a week to get it working again......