Can open small ASCII file, but not large binary file?

I am using the below code to open a large (5.1GB) binary file in MSVC on Windows. The problem is the length is being retrieved as zero. However, when I change the file_path to a smaller ASCII file the code works fine.

Why can I not load the large binary file?

FILE * pFile;
long lSize;
char * buffer;
size_t result;

pFile = fopen(file_path, "rb");
if (pFile == NULL) { 
    fputs("File error", stderr); exit(1); 
}

// obtain file size:
fseek(pFile, 0, SEEK_END);
lSize = ftell(pFile);                                // RETURNS ZERO
rewind(pFile);

// allocate memory to contain the whole file:
buffer = (char*)malloc(sizeof(char)*lSize);
if (buffer == NULL) {
    fputs("Memory error", stderr); exit(2); 
}

// copy the file into the buffer:
result = fread(buffer, 1, lSize, pFile);             // RETURNS ZERO TOO
if (result != lSize) {                               // THIS FAILS
    fputs("Reading error", stderr); exit(3); 
}

/* the whole file is now loaded in the memory buffer. */

its not the file permissions or anything, they are fine.