Hello,
I've tried google and using the forum search but haven't found anyone with the same error I am seeing. Hope someone here knows what i'm doing wrong 
Server runs fine and other mods (that I've tried so far) work fine EXCEPT IC2.
Details:
MC Version: 1.8.9
Forge Version: 1.8.9-11.15.1.1855
OptiFine 1.8.9 - HD_U_H5-
I have tried both 2.3.187 and 2.2.820, with 2.2.820 I get a ton of different errors and the server will not start. With version 2.3.187 the server will start but IC2 will not work.
I have also tried with and without the api.jar file for both versions but I get the same results.
The errors below occur when trying to start the server using 2.3.187:
Display Spoiler
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/INFO] [FML]: Forge Mod Loader has identified 24 mods to load11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: ****************************************
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * The API IC2API from source /mods/industrialcraft-2-2.3.187-ex18 (1).jar is loaded from an incompatible classloader. THIS WILL NOT WORK!
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager$APIContainer.validate(ModAPIManager.java:94)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager.registerDataTableAndParseAPI(ModAPIManager.java:154)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager.manageAPI(ModAPIManager.java:212)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:489)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:87)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:320)...
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: ****************************************
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: ****************************************
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * The API IC2API from source /mods/industrialcraft-2-2.3.187-ex18 (1).jar is loaded from an incompatible classloader. THIS WILL NOT WORK!
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager$APIContainer.validate(ModAPIManager.java:94)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager.registerDataTableAndParseAPI(ModAPIManager.java:154)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager.manageAPI(ModAPIManager.java:212)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:489)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:87)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:320)...
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: ****************************************
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: ****************************************
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * The API IC2API from source /mods/industrialcraft-2-2.3.187-ex18 (1).jar is loaded from an incompatible classloader. THIS WILL NOT WORK!
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager$APIContainer.validate(ModAPIManager.java:94)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager.registerDataTableAndParseAPI(ModAPIManager.java:154)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.ModAPIManager.manageAPI(ModAPIManager.java:212)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:489)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:87)
11.04 17:01:41 [Server] INFO [17:01:41] [Server thread/WARN] [FML]: * at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:320)...
Any help is greatly appreciated!