'groups' error for permissions.yml

2014-02-04 00:12:30 [SEVERE] Permission node 'groups' in permissions.yml is invalid
java.lang.IllegalArgumentException: 'default' key contained unknown value
    at org.bukkit.permissions.Permission.loadPermission(Permission.java:269)
    at org.bukkit.permissions.Permission.loadPermissions(Permission.java:218)
    at org.bukkit.craftbukkit.v1_6_R3.CraftServer.loadCustomPermissions(CraftServer.java:686)
    at org.bukkit.craftbukkit.v1_6_R3.CraftServer.enablePlugins(CraftServer.java:265)
    at net.minecraft.server.MinecraftServer.func_71243_i(MinecraftServer.java:525)
    at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:489)
    at net.minecraft.server.MinecraftServer.func_71247_a(MinecraftServer.java:432)
    at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:224)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:634)
    at net.minecraft.server.ThreadMinecraftServer.run(ThreadMinecraftServer.java:16)