Hi guys...I've found on google some people with the same problem, but all of them have a partial solution...
In practice this error happens where I include a .h file which contain the directive

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
and the macro
BOOST_CLASS_EXPORT()

in more than one .cpp file...
I have the necessity to serialize/deserialize in more than one .cpp file and at these points I have to
include the .h which contains the polymorphic struct that I have to serialize/deserialize. So the partial solution proposed from others to put all the 
the include in a single file, is not praticable for me..
Do you know another solution?thank you very much...
Bye..