diff --git a/plugins/pyloader/src/builtin-policies/rr_priority.py b/plugins/pyloader/src/builtin-policies/rr_priority.py
index 7942ab6..e1d11ac 100644
--- a/plugins/pyloader/src/builtin-policies/rr_priority.py
+++ b/plugins/pyloader/src/builtin-policies/rr_priority.py
@@ -29,7 +29,7 @@ class rr_priority(CPUPolicy) :
     def configure(self):
         param = self.get_parameters()
         param.register_int("Time slice", 1, 10000, True, 2)
-        param.register_int("Is preemptive?", 0, 1, True, 0)
+        param.register_int("Is preemptive?", 0, 1, True, 1)
 
     def is_preemptive(self):
         value = self.get_parameters().get_int("Is preemptive?")
diff --git a/src/backend/cpu_policies_gatekeeper.cc b/src/backend/cpu_policies_gatekeeper.cc
index 2637cdc..f85d143 100644
--- a/src/backend/cpu_policies_gatekeeper.cc
+++ b/src/backend/cpu_policies_gatekeeper.cc
@@ -109,15 +109,23 @@ CPUPoliciesGatekeeper::activate_policy(History *history, CPUPolicy* policy)
   {
     try
     {
-      policy->activate();
+      // policy->activate() needs already an active policy, because:
+      //   * it calls the configure() method on the 
+      //     insert-your-favourite-scripting-language-here-policy
+      //   * which in turn calls the configure() method in the 
+      //     code written by the user
+      //   * which probably uses Simulation to get the _active_ C++ policy,
+      //     so it can get its policy_parameters()
+      //  ... so **DON'T** play Mr. Clever Dick and swap the following two
+      //    lines in an optimization frenzy! Or the user policy WILL fail.
       _active_policies[history] = policy;
+      policy->activate();
     }
     catch(const CPUPolicyException& e)
     {
-      //FIXME what to do here???
-      //probably throwing again a MalformedPolicyException
-      //maybe the best idea. or can we just fallback
-      //to the previous policy?
+      // See the comment above to understand why we do this
+      // in this way
+      _active_policies.erase(_active_policies.find(history));
     }
   }
 }
diff --git a/src/backend/scheduler.cc b/src/backend/scheduler.cc
index 92e9012..f248a86 100644
--- a/src/backend/scheduler.cc
+++ b/src/backend/scheduler.cc
@@ -22,7 +22,7 @@
 #include "concrete_history.hh"
 #include "cpu_policy.hh"
 #include "scheduler.hh"
-#include "user_interrupt_exception.hh"
+#include "cpu_policy_exception.hh"
 
 // Do not include full template definition in the header file
 #include "singleton.tcc"
@@ -71,14 +71,6 @@ Scheduler::get_policy()
 //.............................................................................
 
 
-static bool
-validate_environment(ConcreteEnvironment& e)
-{
-	return true;
-}
-
-
-
 	// Introduces newly arrived processes.
 	// Postcondition:
 	// for each process p in next_snapshot
@@ -542,21 +534,6 @@ check_if_simulation_is_terminated(unsigned int front, auto_ptr<ConcreteEnvironme
 }
 
 
-static void
-print_queue(unsigned int front, auto_ptr<ConcreteEnvironment>& next_snapshot)
-{
-	ReadyQueue& queue = next_snapshot->get_sorted_queue();
-	for(unsigned int i = 0; i < queue.size(); i++)
-	{
-		std::cout << queue.get_item_at(i).get_name();
-	}
-}
-
-
-
-
-
-
 static bool
 try_to_run(unsigned int front, auto_ptr<ConcreteEnvironment>& next_snapshot)
 {
@@ -731,7 +708,7 @@ Scheduler::step_forward(ConcreteHistory& concrete_history, CPUPolicy& cpu_policy
 
 		return !terminated; // watch out for the !
 	}
-	catch(UserInterruptException& e)
+	catch(CPUPolicyException& e)
 	{
 		// Reset values that the policy doesn't need anymore
 		_policy      = NULL;