ALERTING MESSAGEC SCANNING DME FAIL

Got this one about FL070 landing at SBCY... SCANNING DME FAILFCOM2 10.60.8:ALERTING MESSAGE SCANNING DME FAILCAUSE Inputs from both frequency scanning DME radios have failed.CORRECTIVE ACTION Clear the message and check position. Radio updating of FMC position is not available. I did the CORRECTIVE ACTION and the position were OK. The distance to ILS were correct but the VNAV was unable to reach at 2100 FT at FAF, the only restriction on the approach.Someting to do with the dme fail or just coincidence? I have made this approach several times and was the first time that the VNAV was unable to reach FAF at correct altitude... winds less them 8 kt all the way down and i was at the VNAV path before the dme fails appears.Or more like a human fail... like i have been so committed to find about the dme fail that i just have no pay attention to descend?Wat are the influence of this fail in others systems and functions?Thanks and sorry about the english.