interesting. if powerline networking is anything like X10 (oy!), it may be sensitive to how your home's power lines are laid out. i'm guessing each end of the connection is on a different circuit. my first question would be if these two circuits are on the same phase leg of your power panel. if you look in your breaker panel, are the breakers for these two circuits on the same side, or on opposite sides? you may have problems with connections across phases.

also, powerline networking might be sensitive to noise on the powerlines, from refrigerator motors, halogen lights, or even power strips. be glad that you found an outlet in the room that worked.

--dan.