I found my two errors were causing to fail INS DME update.

After completion of VOR?DME elevation entry (3+9) you have  turn knob to  Way point Distance and verify  loaded distance=DME distance. Then press Waypoint Distance on,then press waypoint number where yo insert the coordinates, THEN Press INSERT to Light OFF. (Some reason I wasn't pressing insert off, therefore DME update was falling, then some times I was  selecting WAYP and DIS/TIME . This is another way failing the DME update.)
Now I am careful about these two mistakes, DME update working well.