could this be the reason?

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@2548 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/FilePath.java

@@ -176,6 +176,8 @@ public final class FilePath implements Serializable {
                     zip.closeEntry();
                 }
             }
+            
+            private static final long serialVersionUID = 1L;
         });
     }