SLDRT build error Vicon stream acquisition

I'm trying to get UDP stream coming from a motion capture system (Vicon) so that I can get the position of my robot in real time but I'm having trouble building my model.

I configured my model to External, using rtwin.tlc system target file.

I'm using ViconBlock [http://www.gipsa-lab.fr/projet/RT-MaG/download/Vicon/ViconBlock.pdf] to receive the Udp stream (I have followed the steps in the documentation) and here is the error I get when building:

../Client.h:34:10: fatal error: 'string' file not found
#include <string>
         ^
1 error generated.
gmake: *** [SfunCPP_RecoverVicon_SDK.obj] Error 1

Any ideas on how to build it properly?