Satellite API method system.getDetails() is failing with xml.parsers.expat.ExpatError after upgrading to Satellite 5.6

Issue

• Since upgrading to Satellite 5.6 our script using the system.getDetails API method is failing with the following error:

Traceback (most recent call last):
  File "./getDetails.py", line 12, in <module>
    print sat.system.getDetails(key, 1000013342)
  File "/usr/lib64/python2.6/xmlrpclib.py", line 1199, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib64/python2.6/xmlrpclib.py", line 1489, in __request
    verbose=self.__verbose
  File "/usr/lib64/python2.6/xmlrpclib.py", line 1253, in request
    return self._parse_response(h.getfile(), sock)
  File "/usr/lib64/python2.6/xmlrpclib.py", line 1387, in _parse_response
    p.feed(response)
  File "/usr/lib64/python2.6/xmlrpclib.py", line 601, in feed
    self._parser.Parse(data, 0)
xml.parsers.expat.ExpatError: XML or text declaration not at start of entity: line 1, column 76

• The systemgroup.listSystems() API method is failing with a similar error
• Perl scripts using these methods fail with a similar error:

xml declaration not at start of external entity at line 1, column 76, byte 76 at /usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/XML/Parser.pm line 187