minor error message changes

pycroscopy/io/translators/igor_ibw.py

@@ -59,7 +59,7 @@ class IgorIBWTranslator(Translator):
         else:
             h5_path = append_path
             if not path.exists(append_path):
-                raise Exception('Improper file')
+                raise Exception('File does not exist. Check pathname.')
             h5_file = h5py.File(h5_path, 'r+')
         
 

pycroscopy/io/translators/pifm.py

@@ -194,6 +194,8 @@ class PiFMTranslator(Translator):
                 self.h5_f = h5py.File(h5_path, mode='w')
 
         else:
+            if not os.path.exists(append_path):
+                raise Exception('File does not exist. Check pathname.')
             self.h5_f = h5py.File(append_path, mode='r+')
 
         self.h5_meas_grp = usid.hdf_utils.create_indexed_group(self.h5_f, grp_name)