Index: org/exolab/castor/builder/TypeConversion.java
===================================================================
--- org/exolab/castor/builder/TypeConversion.java	(Revision 6759)
+++ org/exolab/castor/builder/TypeConversion.java	(Arbeitskopie)
@@ -177,8 +177,16 @@
             base = (SimpleType) base.getBaseType();
         }
 
+        SimpleType common = null;
         if (simpleType.getStructureType() == Structure.UNION) {
-            SimpleType common = findCommonType((Union) simpleType);
+            SimpleType currentUnion = simpleType;
+            common = findCommonType((Union) currentUnion);
+            while (common == null 
+                    && currentUnion.getBaseType().getStructureType() == Structure.UNION)
+            {
+                currentUnion = (SimpleType) currentUnion.getBaseType();
+                common = findCommonType((Union) currentUnion);
+            }
             if (common == null) {
                 return new XSClass(SGTypes.OBJECT);
             }