xalan-c 1.10 problem with XalanTransformer.transform

Hello,
I have a problem with transforming a few streams. First stream always goes
correctly, while second is transforming, I receive:

XSLT Warning: Fatal Error.Occurred at unknown file, line 1, column 1. Invalid
document structure (line 1, column 1.)
SAXParseException: Invalid document structure (, line 1, column 1)

Why ? What's wrong with my code ?

void generate_traces(
            const std::string targetIP,
            unsigned iterationsNumber,
            unsigned connectionsNumber,
            unsigned instancesNumber,
            const std::string traceType,
            const std::string dir,
            unsigned sleepTime,
            const std::string traceMode,
            unsigned isBinary = 0
            )
{
   XmlPlatformJanitor xercesJanitor;
   xalanc::XalanTransformer::initialize();
   xalanc::XalanTransformer theXalanTransformer;

   std::list<std::string> contentList;
   if (fs::is_directory(dir))
   {
      std::string tempString;
      for (fs::directory_iterator itr(dir); itr!=fs::directory_iterator();
++itr)
      {
            if (fs::is_regular_file(itr->status()) && strcmp(itr-


            {
               std::cout << itr->path().filename() << ' ' << itr-


               std::ifstream ifs(itr->path().string().c_str());
               contentList.push_front(tempString.assign(
(std::istreambuf_iterator<char>(ifs)), (std::istreambuf_iterator<char>()) ));
            }
      }
   }

   // stream xsl
   std::stringstream xsl_stream(std::stringstream::in | std::stringstream::out);
   xsl_stream << pmtrace::generateXsl<pmtrace::MsgReport>();

   xalanc::XSLTInputSource xslIn(xsl_stream);
   std::list< std::list<std::string> > streamsList;
   std::list<std::string> streamList;

   //generating data streams
   for (int i=0; i<instancesNumber; i++)
   {
      std::string uniqueMccMncId = get_number_full_string();
      std::string uniqueTraceId = get_number_full_string();
      for (std::list<std::string>::const_iterator it = contentList.begin(); it
!= contentList.end(); ++it)
      {
         std::stringstream result_stream(std::stringstream::in |
std::stringstream::out);
         std::stringstream tempstream(std::stringstream::in |
std::stringstream::out);

         std::string s = *it;

         tempstream << s;

         xalanc::XSLTInputSource xmlIn(tempstream);

         xalanc::XSLTResultTarget xmlOut(result_stream);

         int theResult = theXalanTransformer.transform(xmlIn, xslIn, xmlOut);
         if(theResult != 0)
         {
            std::cout << theXalanTransformer.getLastError() << std::endl;
         }

         streamList.push_back(result_stream.str());
      }
      streamsList.push_back(streamList);
      streamList.clear();
   }

   //print_list_of_list_of_string(streamsList);
   std::cout << "Size: " << streamsList.size() << "\n";

   xalanc::XalanTransformer::terminate();
   xalanc::XalanTransformer::ICUCleanUp();
}