Hi! 
  
I'm trying to follow the Using Access Transformers tutorial on the wiki. But once i got the jar file copied to the coremods folder, the console says:  
  
 
[sEVERE] [ForgeModLoader] The coremod xy.jar does not contain a valid jar manifest- it will be ignored
 
  
I've double checked the content of /META-INF/MANIFEST.MF and according to the tutorial it is correct. 
  
 
Manifest-Version: 1.0
FMLCorePlugin: jumika.minecraft.vitalchanges.LoadingPluginVitalChanges
 
  
I have a class named LoadingPluginVitalChanges that implements IFMLLoadingPlugin in the package jumika.minecraft.vitalchanges.