HELP Whenever I install Minecraft forge API on my server I get this error:

[SEVERE] Unexpected exception
java.lang.RuntimeException: ModLoader
at ModLoader.ThrowException(ModLoader.java:1241)
at ModLoader.Init(ModLoader.java:1301)
at net.minecraft.server.MinecraftServer.s(MinecraftServer.java:103)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:315)
at cz.run(SourceFile:465)
Caused by: java.lang.NoSuchMethodException: ft.getNextWidowId()
at java.lang.Class.getDeclaredMethod(Unknown Source)
at ModLoader.Init(ModLoader.java:1279)
... 3 more
PLEASE HELP