error prisonrankup

[13:44:38] [Server thread/ERROR]: Permission node 'prisonrankup.*' in permissions.yml is invalid
java.lang.IllegalArgumentException: Child 'prisonrankup.set' contains invalid value
	at org.bukkit.permissions.Permission.extractChildren(Permission.java:337) ~[server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at org.bukkit.permissions.Permission.loadPermission(Permission.java:306) ~[server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at org.bukkit.permissions.Permission.loadPermissions(Permission.java:232) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at org.bukkit.craftbukkit.v1_7_R1.CraftServer.loadCustomPermissions(CraftServer.java:824) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at org.bukkit.craftbukkit.v1_7_R1.CraftServer.enablePlugins(CraftServer.java:383) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.m(MinecraftServer.java:342) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.g(MinecraftServer.java:319) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.a(MinecraftServer.java:275) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at net.minecraft.server.v1_7_R1.DedicatedServer.init(DedicatedServer.java:175) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java:424) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
	at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:617) [server.jar:git-Bukkit-1.7.2-R0.3-b3020jnks]
[13:44:38] [Server thread/INFO]: Done (36.187s)! For help, type "help" or "?"