Always for ML mods into "public" class accessibility - we don't call from the default package like ML does.

common/cpw/mods/fml/common/ModClassLoader.java

@@ -23,6 +23,9 @@ import java.util.logging.Level;
 
 import com.google.common.collect.ImmutableList;
 
+import cpw.mods.fml.common.asm.ASMTransformer;
+import cpw.mods.fml.common.asm.transformers.AccessTransformer;
+import cpw.mods.fml.common.modloader.BaseModProxy;
 import cpw.mods.fml.relauncher.RelaunchClassLoader;
 
 /**
@@ -76,4 +79,11 @@ public class ModClassLoader extends URLClassLoader
     {
         return STANDARD_LIBRARIES;
     }
+
+    public Class<? extends BaseModProxy> loadBaseModClass(String modClazzName) throws Exception
+    {
+        AccessTransformer transformer = (AccessTransformer)mainClassLoader.getTransformers().get(0);
+        transformer.ensurePublicAccessFor(modClazzName);
+        return (Class<? extends BaseModProxy>) Class.forName(modClazzName, true, this);
+    }
 }

common/cpw/mods/fml/common/asm/transformers/AccessTransformer.java

@@ -408,4 +408,11 @@ public class AccessTransformer implements IClassTransformer
             }
         }
     }
+    public void ensurePublicAccessFor(String modClazzName)
+    {
+        Modifier m = new Modifier();
+        m.setTargetAccess("public");
+        m.modifyClassVisibility = true;
+        modifiers.put(modClazzName, m);
+    }
 }

common/cpw/mods/fml/common/modloader/ModLoaderModContainer.java

@@ -17,6 +17,7 @@ import java.io.File;
 import java.io.FileReader;
 import java.io.FileWriter;
 import java.io.IOException;
+import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
@@ -485,10 +486,12 @@ public class ModLoaderModContainer implements ModContainer
             EnumSet<TickType> ticks = EnumSet.noneOf(TickType.class);
             this.gameTickHandler = new BaseModTicker(ticks, false);
             this.guiTickHandler = new BaseModTicker(ticks.clone(), true);
-            Class<? extends BaseModProxy> modClazz = (Class<? extends BaseModProxy>) Class.forName(modClazzName, true, modClassLoader);
+            Class<? extends BaseModProxy> modClazz = (Class<? extends BaseModProxy>) modClassLoader.loadBaseModClass(modClazzName);
             configureMod(modClazz, event.getASMHarvestedData());
             isNetworkMod = FMLNetworkHandler.instance().registerNetworkMod(this, modClazz, event.getASMHarvestedData());
-            mod = (BaseModProxy)modClazz.newInstance();
+            Constructor<? extends BaseModProxy> ctor = modClazz.getConstructor();
+            ctor.setAccessible(true);
+            mod = modClazz.newInstance();
             if (!isNetworkMod)
             {
                 FMLLog.fine("Injecting dummy network mod handler for BaseMod %s", getModId());

common/cpw/mods/fml/relauncher/RelaunchClassLoader.java

@@ -7,6 +7,7 @@ import java.net.URL;
 import java.net.URLClassLoader;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -175,4 +176,9 @@ public class RelaunchClassLoader extends URLClassLoader
             return new byte[0];
         }
     }
+
+    public List<IClassTransformer> getTransformers()
+    {
+        return Collections.unmodifiableList(transformers);
+    }
 }