fix error msg formatting in krb function

Script/CastorScript.py

@@ -385,7 +385,7 @@ def krb_tokenexpiration(logger):
         expiration_date = datetime.datetime.strptime(' '.join(ticket[2:4]),
                 '%m/%d/%y %H:%M:%S')
     except ValueError as exc:
-        logger.critical('error converting string to date: ticket="{}", date_string="{}"',
+        logger.critical('error converting string to date: ticket="%s", date_string="%s"',
                 ticket,  ' '.join(ticket[2:4]))
         raise exc
     return expiration_date