If it works on lines 2, 3, and 4, but not on 1 and 5, it sounds like you've got polarity problems going all the way back to your frame. Depends on how correct you want to be about it, I guess. If it were my setup, I'd start at the frame and make sure it was consistent there, then polarity guards would be irrelevant. I had a problem when I was setting up my system, as just described in another thread, where some of my sources of dial tone just came with the polarity backwards. Since they are all voip devices, and all have modular jacks, I could take the modular plug out of one and stick it in another and the polarity would be reversed. (Meaning I didn't have the wiring of the modular cords as a variable.) So where all the lines from these devices appear at my "CO block", I've straightened out the polarity there, so from there on through they are all correct. Just my 2 cents.
