Missing cricket graph for some switch ?

Hi.. Missing cricket graph for one type of switch ? Installed nav 3.7.1 on Debian (5.0.7) machine. On some switch, the files "navTargets" is empty /etc/nav/cricket-config/switch-ports/10.70.11.17/navTargets When I add data in then file manually, then graphs are presented but the graph disappears again after a while... file is overwritten and empty again. -Tor