diff --git a/nova/api/openstack/wsgi.py b/nova/api/openstack/wsgi.py
index 6ab4f63cfc3..e440889a0da 100644
--- a/nova/api/openstack/wsgi.py
+++ b/nova/api/openstack/wsgi.py
@@ -654,11 +654,12 @@ def __exit__(self, ex_type, ex_value, ex_traceback):
             return True
 
         if isinstance(ex_value, exception.NotAuthorized):
-            msg = unicode(ex_value)
+            msg = unicode(ex_value.message % ex_value.kwargs)
             raise Fault(webob.exc.HTTPForbidden(explanation=msg))
         elif isinstance(ex_value, exception.Invalid):
+            msg = unicode(ex_value.message % ex_value.kwargs)
             raise Fault(exception.ConvertedException(
-                code=ex_value.code, explanation=unicode(ex_value)))
+                    code=ex_value.code, explanation=msg))
 
         # Under python 2.6, TypeError's exception value is actually a string,
         # so test # here via ex_type instead:
@@ -1167,6 +1168,10 @@ def __call__(self, req):
         # Replace the body with fault details.
         code = self.wrapped_exc.status_int
         fault_name = self._fault_names.get(code, "computeFault")
+        explanation = self.wrapped_exc.explanation
+        LOG.debug(_("Returning %(code)s to user: %(explanation)s"),
+                  {'code': code, 'explanation': explanation})
+
         fault_data = {
             fault_name: {
                 'code': code,
diff --git a/nova/exception.py b/nova/exception.py
index fe80ca25f87..ab275e2e599 100644
--- a/nova/exception.py
+++ b/nova/exception.py
@@ -387,6 +387,7 @@ class InvalidDevicePath(Invalid):
 
 class DevicePathInUse(Invalid):
     message = _("The supplied device path (%(path)s) is in use.")
+    code = 409
 
 
 class DeviceIsBusy(Invalid):