diff --git a/ucscsdk/ucscmethodfactory.py b/ucscsdk/ucscmethodfactory.py
index a824945..fc13664 100644
--- a/ucscsdk/ucscmethodfactory.py
+++ b/ucscsdk/ucscmethodfactory.py
@@ -871,7 +871,7 @@ def config_resolve_class_sorted(cookie, class_id, in_filter, in_size, in_hierarc
     return xml_request
 
 
-def config_resolve_classes(cookie, in_ids, in_return_count_only, in_hierarchical=YesOrNo.FALSE):
+def config_resolve_classes(cookie, in_ids, in_return_count_only=None, in_hierarchical=YesOrNo.FALSE):
     """ Auto-generated UCSC XML API Method. """
     method = ExternalMethod("ConfigResolveClasses")
 
diff --git a/ucscsdk/ucscsession.py b/ucscsdk/ucscsession.py
index 83549de..a700e54 100755
--- a/ucscsdk/ucscsession.py
+++ b/ucscsdk/ucscsession.py
@@ -247,7 +247,13 @@ def post_elem(self, elem, dme="central-mgr"):
         self.dump_xml_request(elem)
         xml_str = xc.to_xml_str(elem)
 
-        response_str = self.post_xml(xml_str, dme=dme)
+        response_str = ""
+        try:
+            response_str = self.post_xml(xml_str, dme=dme)
+        except:
+            self._tx_lock_release_conditional(elem)
+            raise
+
         self.dump_xml_response(response_str)
 
         try: