Issue with XStream jar while migrating from WAS 6.1 to WAS 7.0

We were using xstream-1.2.jar with WAS 6.1
When we migrated our application from WAS 6.1 to WAS 7.0, xstream-1.2.jar was throwing exception. To resolve this exception, we upgraded to xstream-1.3.1.jar but getting following exception:

Exception in thread "main" com.thoughtworks.xstream.converters.ConversionException: Invalid reference

Also we are getting null pointer exception in canConvert(Object class) method of convertor. Here parameter class is coming as null. As per our analysis, this method is called by XStream framework internally.

When we looked into Stream jar code, came to following part which was throwing exception:

final Object result;
String attributeName = getMapper().aliasForSystemAttribute("reference");
String reference = attributeName == null ? null : reader.getAttribute(attributeName);
if (reference != null) {
result = values.get(getReferenceKey(reference));
if (result == null)

}
When we searched XStream user mailing list, got a similar issue at following URL:
http://comments.gmane.org/gmane.comp.java.xstream.user/6103

We tried to implement solution given in this thread like but did not get expected results.

Please advice.