Hello , I've made made a modpack including BoP, to run on a 1.5.2 server , but when i run the server, it gives me this error :

22:48:48 [severe] java.lang.ClassNotFoundException: biomesoplenty.mobs.EntityJungleSpider
22:48:48 [severe] at cpw.mods.fml.relauncher.RelaunchClassLoader.findClass(RelaunchClassLoader.java:273)
22:48:48 [severe] at java.lang.ClassLoader.loadClass(Unknown Source)
22:48:48 [severe] at java.lang.ClassLoader.loadClass(Unknown Source)
22:48:48 [severe] at java.lang.Class.forName0(Native Method)
22:48:48 [severe] at java.lang.Class.forName(Unknown Source)
22:48:48 [severe] at powercrystals.minefactoryreloaded.modhelpers.biomesoplenty.BiomesOPlenty.load(BiomesOPlenty.java:119)
22:48:48 [severe] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
22:48:48 [severe] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
22:48:48 [severe] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
22:48:48 [severe] at java.lang.reflect.Method.invoke(Unknown Source)
22:48:48 [severe] at cpw.mods.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:494)
22:48:48 [severe] at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
22:48:48 [severe] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
22:48:48 [severe] at java.lang.reflect.Method.invoke(Unknown Source)
22:48:48 [severe] at com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:74)
22:48:48 [severe] at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
22:48:48 [severe] at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)
22:48:48 [severe] at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
22:48:48 [severe] at com.google.common.eventbus.EventBus.post(EventBus.java:267)
22:48:48 [severe] at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadController.java:192)
22:48:48 [severe] at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:172)
22:48:48 [severe] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
22:48:48 [severe] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
22:48:48 [severe] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
22:48:48 [severe] at java.lang.reflect.Method.invoke(Unknown Source)
22:48:48 [severe] at com.google.common.eventbus.EventHandler.handleEvent(EventHandler.java:74)
22:48:48 [severe] at com.google.common.eventbus.SynchronizedEventHandler.handleEvent(SynchronizedEventHandler.java:45)
22:48:48 [severe] at com.google.common.eventbus.EventBus.dispatch(EventBus.java:314)
22:48:48 [severe] at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:296)
22:48:48 [severe] at com.google.common.eventbus.EventBus.post(EventBus.java:267)
22:48:48 [severe] at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:103)
22:48:48 [severe] at cpw.mods.fml.common.Loader.initializeMods(Loader.java:691)
22:48:48 [severe] at cpw.mods.fml.server.FMLServerHandler.finishServerLoading(FMLServerHandler.java:93)
22:48:48 [severe] at cpw.mods.fml.common.FMLCommonHandler.onServerStarted(FMLCommonHandler.java:355)
22:48:48 [severe] at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:168)
22:48:48 [severe] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:574)
22:48:48 [severe] at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:573)
22:48:48 [severe] Caused by: java.lang.NullPointerException
22:48:48 [severe] at org.objectweb.asm.ClassReader.(ClassReader.java:153)
22:48:48 [severe] at miscperipherals.asm.ImplementIfLoadedTransformer.transform(ImplementIfLoadedTransformer.java:19)
22:48:48 [severe] at cpw.mods.fml.relauncher.RelaunchClassLoader.runTransformers(RelaunchClassLoader.java:387)
22:48:48 [severe] at cpw.mods.fml.relauncher.RelaunchClassLoader.findClass(RelaunchClassLoader.java:260)
22:48:48 [severe] ... 36 more

The server works fine with this error , but i would like to solve it , thank you.

Please don't report bugs if you're using 1.5.2 versions. They're long outdated and we have no intentions of revisiting them to fix bugs.

That's a problem with MFR using outdated API. Don't worry, you can play with it, it's nothing serious, and the support for MFR was moved to BOP.