I switched to a new map and did /dynmap purgeworld to all worlds i had. Here the error I get:

2013-07-03 12:40:53 [WARNING] [Dynmap-GriefPrevention] Task #47 for Dynmap-GriefPrevention v0.40 generated an exception
java.lang.ClassCastException: me.ryanhamshire.GriefPrevention.ClaimArray cannot be cast to java.util.ArrayList
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin.updateClaims(DynmapGriefPreventionPlugin.java:239)
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin.access$000(DynmapGriefPreventionPlugin.java:34)
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin$GriefPreventionUpdate.run(DynmapGriefPreventionPlugin.java:94)
at org.bukkit.craftbukkit.v1_6_R1.scheduler.CraftTask.run(CraftTask.java:58)
at org.bukkit.craftbukkit.v1_6_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345)
at net.minecraft.server.v1_6_R1.MinecraftServer.t(MinecraftServer.java:518)
at net.minecraft.server.v1_6_R1.DedicatedServer.t(DedicatedServer.java:235)
at net.minecraft.server.v1_6_R1.MinecraftServer.s(MinecraftServer.java:481)
at net.minecraft.server.v1_6_R1.MinecraftServer.run(MinecraftServer.java:413)
at net.minecraft.server.v1_6_R1.ThreadServerApplication.run(SourceFile:582)

What version of GriefPrevention are you running? Please try newest Dynmap-GriefPrevention release if it's a recent one.

I have similar error:
2013-07-12 15:05:58 [WARNING] [Dynmap-GriefPrevention] Task #29 for Dynmap-GriefPrevention v0.70 generated an exception
java.lang.NoSuchMethodError: me.ryanhamshire.GriefPrevention.Claim.getPermissions(Ljava/util/ArrayList;Ljava/util/ArrayList;Ljava/util/ArrayList;Ljava/util/ArrayList;)V
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin.formatInfoWindow(DynmapGriefPreventionPlugin.java:117)
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin.handleClaim(DynmapGriefPreventionPlugin.java:224)
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin.updateClaims(DynmapGriefPreventionPlugin.java:263)
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin.access$000(DynmapGriefPreventionPlugin.java:35)
at org.dynmap.griefprevention.DynmapGriefPreventionPlugin$GriefPreventionUpdate.run(DynmapGriefPreventionPlugin.java:99)
at org.bukkit.craftbukkit.v1_6_R2.scheduler.CraftTask.run(CraftTask.java:58)
at org.bukkit.craftbukkit.v1_6_R2.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345)
at net.minecraft.server.v1_6_R2.MinecraftServer.t(MinecraftServer.java:518)
at net.minecraft.server.v1_6_R2.DedicatedServer.t(DedicatedServer.java:239)
at net.minecraft.server.v1_6_R2.MinecraftServer.s(MinecraftServer.java:481)
at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java:413)
at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:582)

I have tried with both 0.60 and 0.70 using Dynmap 1.8 and GriefPrevention build 126 and 127. I suspect your using the old API for GP and after the rewrite I suspect things have changed.

I only support versions published (d.b.o or otherwise). Dev builds aren't supported.

I'll look at updating the dev build of Dynmap-GP to use the dev builds, but will not release until their is a corresponding release of GP