help needed for RTOS Programming

[Jyothi@Pic]

Hi,

I am learning to program RTOS in keil microvision3 RTX51 Tiny

i have selected the device as AT89s52 and the program is as below

#include <rtx51tny.h>


int counter0;
int counter1;
void job0 (void) _task_ 0 {
os_create_task (1); /* mark task 1 as ready */
while (1) { /* loop forever */
counter0++; /* update the counter */
}
}
void job1 (void) _task_ 1 {
while (1) { /* loop forever */
counter1++; /* update the counter */
}
}

I have included the header file and i can view the file also but it is giving the error as

*** FATAL ERROR L210: I/O ERROR ON INPUT FILE:
EXCEPTION 0021H: PATH OR FILE NOT FOUND
FILE: C:\KEIL\C51\LIB\RTX51.LIB


what am i suppose to do how to get that file somebody help