OpenCv No rule to make target

this is my first example with OpenCv:

 #include <stdlib.h> #include <stdio.h> #include <math.h> #include "opencv/cv.h" #include "opencv/highgui.h" int main(int argc, char *argv[]) { IplImage* img = 0; img=cvLoadImage("/home/michele/Pictures/sensor.png"); // carica l'immagine cvNamedWindow("mainWin", CV_WINDOW_AUTOSIZE); // crea la finestra cvShowImage("mainWin", img ); // mostra l'immagine cvWaitKey(0); // wait for a key cvReleaseImage(&img ); //rilascia l'immagine system("PAUSE"); return 0; } 

If I click on BuildAll I've this error returned:

make: *** No rule to make target `1st.o', needed by `firstOpenCV'. Stop. 

What I have to do?

Thanks.