Fortran - log: SING error

Question

 Fortran  run-time error M6202: MATH - log: SING error  Press any key to continue

 

     DO I=1,6000000

    
        if (y(2).lt.0) then
        B=-RM(J)*Y(2)**P/(2.0*T(1))
        F=1-EXP(B)
       WRITE(*,*)f,Y(2)
        y(2)=SQRT(-2.0*DLOG(F)*T(1)/RM(J))