diff --git a/GPy/core/parameterization/parameter_core.py b/GPy/core/parameterization/parameter_core.py
index d4779127..6a8f1b1d 100644
--- a/GPy/core/parameterization/parameter_core.py
+++ b/GPy/core/parameterization/parameter_core.py
@@ -781,8 +781,8 @@ class Parameterizable(OptimizationHandlable):
         if param in self._parameters_ and index is not None:
             self.remove_parameter(param)
             self.add_parameter(param, index)
-        elif param.has_parent():
-            raise HierarchyError, "parameter {} already in another model ({}), create new object (or copy) for adding".format(param._short(), param._highest_parent_._short())
+        #elif param.has_parent():
+        #    raise HierarchyError, "parameter {} already in another model ({}), create new object (or copy) for adding".format(param._short(), param._highest_parent_._short())
         elif param not in self._parameters_:
             if param.has_parent():
                 parent = param._parent_
diff --git a/GPy/likelihoods/student_t.py b/GPy/likelihoods/student_t.py
index b77296ca..47efd443 100644
--- a/GPy/likelihoods/student_t.py
+++ b/GPy/likelihoods/student_t.py
@@ -43,8 +43,8 @@ class StudentT(Likelihood):
         Pull out the gradients, be careful as the order must match the order
         in which the parameters are added
         """
-        self.sigma2.gradient = derivatives[0]
-        self.v.gradient = derivatives[1]
+        self.sigma2.gradient = grads[0]
+        self.v.gradient = grads[1]
 
     def pdf_link(self, link_f, y, Y_metadata=None):
         """
diff --git a/GPy/testing/mapping_tests.py b/GPy/old_tests/mapping_tests.py
similarity index 100%
rename from GPy/testing/mapping_tests.py
rename to GPy/old_tests/mapping_tests.py