Previously, i loaded the folder containing my all classes (for example the folder Host_Class). I had placed this folder in the path /home/lvuser/natinst/bin/. I.e I will had /home/lvuser/natinst/bin/Host_Class
Now, i place directly my classes in the path /home/lvuser/natinst/bin/ and not via a directory like Host_Class.
Apparently, By default, when RT target runs, the reading is limited only to the path specified in the RT target properties. In my case, this path is /home/lvuser/natinst/bin/