17:44:51 [SEVERE] PLAYER_COMMAND loading DropBuild v1.21 (Is it up to date?)
java.lang.NoSuchFieldError: PLAYER_COMMAND
    at com.recanu.DropBuild.DropBuild.registerEvents(DropBuild.java:88)
    at com.recanu.DropBuild.DropBuild.onEnable(DropBuild.java:69)
    at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:118)
    at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:414)
    at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:187)
    at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:83)
    at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:61)
    at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:204)
    at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:191)
    at net.minecraft.server.MinecraftServer.d(MinecraftServer.java:131)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:246)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:366)