The Mana_PayCost.java file is now an empty class with no real code and just two lines of comments. This takes care of the JAR creation failed message. We may decide to delete this class from the SVN at some point. :)

src/forge/Mana_PayCost.java

@@ -1 +1,10 @@
-// merged with ManaCost since it was a thin wrapper// file NOT deleted to keep SVN history available
+package forge;
+
+public class Mana_PayCost {
+    
+    /**
+     *  Merged with ManaCost since it was a thin wrapper.
+     *  File NOT deleted to keep SVN history available.
+     */
+    
+}