Does Boost.Serialization serialize differently on different platforms?

I use Boost.Serialization to serialize a std::map. The code looks like this

void Dictionary::serialize(std::string & buffer)
{
  try {
    std::stringstream ss;
    boost::archive::binary_oarchive archive(ss);
    archive << dict_; 
    buffer = ss.str();
  } catch (const std::exception & ex) {
    throw DictionaryException(ex.what());
  }
}

void Dictionary::deserialize(const char * const data, int length)
{
  try {
    namespace io = boost::iostreams;
    io::array_source source(data, length);
    io::stream<io::array_source> in(source);
    boost::archive::binary_iarchive archive(in);
    archive >> dict_;
  } catch (const std::exception & ex) {
    throw DictionaryException(ex.what());
  }
}

I compiled and tested the code on a Mac Snow Leopard and on Ubuntu Lucid 10.04. There is Boost 1.40 on both systems. On the Mac I built the code myself. On the Ubuntu box I got the binaries via aptitude.

Problem: When I serialize the map on the Mac I can't deserialize it on the Ubuntu box. I get an invalid signature exception if I try.