diff --git a/GPy/util/datasets.py b/GPy/util/datasets.py
index fdba0ac5..b4a26636 100644
--- a/GPy/util/datasets.py
+++ b/GPy/util/datasets.py
@@ -3,7 +3,6 @@ import numpy as np
 import GPy
 import scipy.io
 import cPickle as pickle
-import urllib as url
 import zipfile
 import tarfile
 import datetime
@@ -15,7 +14,7 @@ except ImportError:
     ipython_available=False
 
 
-import sys, urllib
+import sys, urllib2
 
 def reporthook(a,b,c):
     # ',' at the end of the line is important!
@@ -82,7 +81,18 @@ def download_url(url, store_directory, save_name = None, messages = True, suffix
     print "Downloading ", url, "->", os.path.join(store_directory, file)
     if not os.path.exists(dir_name):
         os.makedirs(dir_name)
-    urllib.urlretrieve(url+suffix, save_name, reporthook)
+    try:
+        response = urllib2.urlopen(url+suffix)
+    except urllib2.URLError, e:
+        if not hasattr(e, "code"):
+            raise
+        response = e
+        if response.code == 404:
+            raise ValueError('Url ' + url + suffix + ' 404 not found.')
+    with open(save_name, 'wb') as f:
+        f.write(response.read())
+    
+    #urllib.urlretrieve(url+suffix, save_name, reporthook)
 
 def authorize_download(dataset_name=None):
     """Check with the user that the are happy with terms and conditions for the data set."""
diff --git a/GPy/util/mocap.py b/GPy/util/mocap.py
index 78f00955..58662cf9 100644
--- a/GPy/util/mocap.py
+++ b/GPy/util/mocap.py
@@ -67,14 +67,14 @@ class tree:
         for i in range(len(self.vertices)):
             if self.vertices[i].id == id:
                 return i
-        raise Error, 'Reverse look up of id failed.'
+        raise ValueError('Reverse look up of id failed.')
 
     def get_index_by_name(self, name):
         """Give the index associated with a given vertex name."""
         for i in range(len(self.vertices)):
             if self.vertices[i].name == name:
                 return i
-        raise Error, 'Reverse look up of name failed.'
+        raise ValueError('Reverse look up of name failed.')
 
     def order_vertices(self):
         """Order vertices in the graph such that parents always have a lower index than children."""
@@ -433,6 +433,8 @@ class acclaim_skeleton(skeleton):
         lin = self.read_line(fid)
         while lin != ':DEGREES':
             lin = self.read_line(fid)
+            if lin == '':
+                raise ValueError('Could not find :DEGREES in ' + fid.name)
 
         counter = 0
         lin = self.read_line(fid)
@@ -443,9 +445,9 @@ class acclaim_skeleton(skeleton):
                 if frame_no:
                     counter += 1
                     if counter != frame_no:
-                        raise Error, 'Unexpected frame number.'
+                        raise ValueError('Unexpected frame number.')
                 else:
-                    raise Error, 'Single bone name  ...'
+                    raise ValueError('Single bone name  ...')
             else:
                 ind = self.get_index_by_name(parts[0])
                 bones[ind].append(np.array([float(channel) for channel in parts[1:]]))
@@ -573,7 +575,7 @@ class acclaim_skeleton(skeleton):
                         return
                     lin = self.read_line(fid)
             else:
-                raise Error, 'Unrecognised file format'
+                raise ValueError('Unrecognised file format')
             self.finalize()
             
     def read_units(self, fid):