CS50 Lab4 : code works fine but check50 fails to compile it

I have a problem on Lab4 of Harvard's CS50 course (intro to CS) My code for Lab4 of CS50 course works well on my laptop but when I run check50 before submitting it, I get the following error code failed to compile. I know it can happen when you modify something else than what you are supposed to on the base code provided by the course but here, I only added code under the TODO comments (It's the least I can do to make it work. I also tried to remove the comments). Here is my code :

// Modifies the volume of an audio file

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

// Number of bytes in .wav header
const int HEADER_SIZE = 44;

int main(int argc, char *argv[])
{
    // Check command-line arguments
    if (argc != 4)
    {
        printf("Usage: ./volume input.wav output.wav factor\n");
        return 1;
    }

    // Open files and determine scaling factor
    FILE *input = fopen(argv[1], "r");
    if (input == NULL)
    {
        printf("Could not open file.\n");
        return 1;
    }

    FILE *output = fopen(argv[2], "w");
    if (output == NULL)
    {
        printf("Could not open file.\n");
        return 1;
    }

    float factor = atof(argv[3]);

    // TODO: Copy header from input file to output file
    u_int8_t header[44];
    fread(&header, HEADER_SIZE, 1, input);
    fwrite(&header, HEADER_SIZE, 1, output);

    // TODO: Read samples from input file and write updated data to output file
    int16_t buffer;
    while (fread(&buffer, sizeof(int16_t), 1, input))
    {
        //Apply the factor to the buffer
        buffer *= factor;
        fwrite(&buffer, sizeof(int16_t), 1, output);
    }

    // Close files
    fclose(input);
    fclose(output);
}

Thanks by advance for any help !