OnTime with Privileges

00:07:42 [WARNING] [OnTime] Task #1099 for OnTime v3.5.0 generated an exception
java.lang.NullPointerException: An invalid default group is defined in config.yml.
        at net.krinsoft.privileges.groups.GroupManager.getDefaultGroup(GroupManager.java:57)
        at net.milkbowl.vault.permission.plugins.Permission_Privileges.playerRemoveGroup(Permission_Privileges.java:142)
        at net.milkbowl.vault.permission.Permission.playerRemoveGroup(Permission.java:572)
        at me.edge209.OnTime.Rewards.Rewards.issue(Rewards.java:1311)
        at me.edge209.OnTime.Rewards.Rewards$1.run(Rewards.java:581)
        at org.bukkit.craftbukkit.scheduler.CraftTask.run(CraftTask.java:53)
        at org.bukkit.craftbukkit.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345)
        at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:514)
        at net.minecraft.server.DedicatedServer.r(DedicatedServer.java:222)
        at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:478)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:413)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:856)