diff -r 7c4e090bc25f -r d5403de0792b server/session.py
--- a/server/session.py	Mon Mar 09 18:02:49 2015 +0100
+++ b/server/session.py	Tue Feb 17 12:43:42 2015 +0100
@@ -971,7 +971,7 @@
     def transaction_uuid(self, set=True):
         uuid = self.transaction_data.get('tx_uuid')
         if set and uuid is None:
-            self.transaction_data['tx_uuid'] = uuid = uuid4().hex
+            self.transaction_data['tx_uuid'] = uuid = unicode(uuid4().hex)
             self.repo.system_source.start_undoable_transaction(self, uuid)
         return uuid