diff --git a/fixtracks/widgets/classifier.py b/fixtracks/widgets/classifier.py
index 407f047..e610a29 100644
--- a/fixtracks/widgets/classifier.py
+++ b/fixtracks/widgets/classifier.py
@@ -247,7 +247,7 @@ class ConsistencyWorker(QRunnable):
             if steps > 0 and f % steps == 0:
                 progress += 1
                 self.signals.progress.emit(progress, processed, errors)
-        self.signals.message.emit("Tracking stopped at frame %i.", f)
+        self.signals.message.emit(f"Tracking stopped at frame {f}.")
         self.signals.stopped.emit(f)
 
 
@@ -548,11 +548,17 @@ class ConsistencyClassifier(QWidget):
             self._tracks = self._dataworker.tracks
             self._dataworker = None
         if np.sum(self._userlabeled) < 1:
-            logging.error("ConsistencyTracker: I need at least 1 user-labeled frame to start with!")
+            msg = "ConsistencyTracker: I need at least 1 user-labeled frame to start with!"
+            logging.error(msg)
+            self._messagebox.append(msg)
             self.setEnabled(False)
         else:
             t1_userlabeled = self._frames[self._userlabeled & (self._tracks == 1)]
             t2_userlabeled = self._frames[self._userlabeled & (self._tracks == 2)]
+            if any([len(t1_userlabeled) == 0, len(t2_userlabeled)== 0]):
+                self._messagebox.append("Error preparing data! Make sure that the first user-labeled frames contain both tracks!")
+                self.setEnabled(False)
+                return
             max_startframe = np.min([t1_userlabeled[-1], t2_userlabeled[-1]])
             min_startframe = np.max([t1_userlabeled[0], t2_userlabeled[0]])
             self._maxframes = np.max(self._frames)
@@ -574,10 +580,7 @@ class ConsistencyClassifier(QWidget):
     def stop(self):
         if self._worker is not None:
             self._worker.stop()
-        self._startbtn.setEnabled(True)
-        self._proceedbtn.setEnabled(True)
-        self._stopbtn.setEnabled(False)
-        self._refreshbtn.setEnabled(True)
+            self._messagebox.append("Stopping tracking.")
 
     def start(self):
         self._startbtn.setEnabled(False)
@@ -590,6 +593,7 @@ class ConsistencyClassifier(QWidget):
         self._worker.signals.progress.connect(self.worker_progress)
         self._worker.signals.message.connect(self.worker_error)
         self._worker.signals.currentframe.connect(self.worker_frame)
+        self._messagebox.append("Tracking in progress ...")
         self.threadpool.start(self._worker)
 
     def worker_frame(self, frame):
@@ -602,8 +606,11 @@ class ConsistencyClassifier(QWidget):
         self.start()
 
     def refresh(self):
+        self.setEnabled(False)
         self._dataworker = ConsitencyDataLoader(self._data)
         self._dataworker.signals.stopped.connect(self.data_processed)
+        self._messagebox.clear()
+        self._messagebox.append("Refreshing...")
         self.threadpool.start(self._dataworker)
 
     def worker_progress(self, progress, processed, errors):
@@ -612,13 +619,15 @@ class ConsistencyClassifier(QWidget):
         self._assignedlabel.setText(str(processed))
 
     def worker_stopped(self, frame):
-        self._apply_btn.setEnabled(True)
         self._startbtn.setEnabled(True)
+        self._proceedbtn.setEnabled(True)
         self._stopbtn.setEnabled(False)
+        self._apply_btn.setEnabled(True)
+        self._refreshbtn.setEnabled(True)
         self._startframe_spinner.setValue(frame-1)
         self._proceedbtn.setEnabled(bool(frame < self._maxframes-1))
-        self._refreshbtn.setEnabled(True)
         self._processed_frames = frame
+        self._messagebox.append("... done.")
 
     def assignedTracks(self):
         return self._tracks
@@ -683,7 +692,7 @@ def main():
     import pickle
     from fixtracks.info import PACKAGE_ROOT
 
-    datafile = PACKAGE_ROOT / "data/merged_small_starter.pkl"
+    datafile = PACKAGE_ROOT / "data/merged_small_beginning.pkl"
 
     with open(datafile, "rb") as f:
         df = pickle.load(f)