diff --git a/lib/galaxy/workflow/scheduling_manager.py b/lib/galaxy/workflow/scheduling_manager.py
index 46764ec3815..a51b06f95cc 100644
--- a/lib/galaxy/workflow/scheduling_manager.py
+++ b/lib/galaxy/workflow/scheduling_manager.py
@@ -283,19 +283,22 @@ class WorkflowRequestMonitor(Monitors):
     def __monitor(self):
         to_monitor = self.workflow_scheduling_manager.active_workflow_schedulers
         while self.monitor_running:
-            if self.invocation_grabber:
-                self.invocation_grabber.grab_unhandled_items()
+            try:
+                if self.invocation_grabber:
+                    self.invocation_grabber.grab_unhandled_items()
 
-            monitor_step_timer = self.app.execution_timer_factory.get_timer(
-                'internal.galaxy.workflows.scheduling_manager.monitor_step',
-                'Workflow scheduling manager monitor step complete.'
-            )
-            for workflow_scheduler_id, workflow_scheduler in to_monitor.items():
-                if not self.monitor_running:
-                    return
+                monitor_step_timer = self.app.execution_timer_factory.get_timer(
+                    'internal.galaxy.workflows.scheduling_manager.monitor_step',
+                    'Workflow scheduling manager monitor step complete.'
+                )
+                for workflow_scheduler_id, workflow_scheduler in to_monitor.items():
+                    if not self.monitor_running:
+                        return
 
-                self.__schedule(workflow_scheduler_id, workflow_scheduler)
-            log.trace(monitor_step_timer.to_str())
+                    self.__schedule(workflow_scheduler_id, workflow_scheduler)
+                log.trace(monitor_step_timer.to_str())
+            except Exception:
+                log.exception('An exception occured scheduling while scheduling workflows')
             self._monitor_sleep(1)
 
     def __schedule(self, workflow_scheduler_id, workflow_scheduler):
diff --git a/tools/filters/secure_hash_message_digest.xml b/tools/filters/secure_hash_message_digest.xml
index 50554c7181d..329f3635351 100644
--- a/tools/filters/secure_hash_message_digest.xml
+++ b/tools/filters/secure_hash_message_digest.xml
@@ -13,14 +13,13 @@
     </command>
     <inputs>
         <param format="data" name="input1" type="data" label="Text file"/>
-        <param name="algorithms" type="select" multiple="True" display="checkboxes" label="Choose the algorithms">
+        <param name="algorithms" type="select" optional="false" multiple="true" display="checkboxes" label="Choose the algorithms">
           <option value="md5"/>
           <option value="sha1"/>
           <option value="sha224"/>
           <option value="sha256"/>
           <option value="sha384"/>
           <option value="sha512"/>
-          <validator type="no_options" message="You must select at least one algorithm." />
         </param>
     </inputs>
     <outputs>