Access .csv file from a dll - dll

Question

I am trying to access a file inside my DLL, but fopen always returns NULL. I am not very familiar with DLL's and I do not know how to debug this problem. I tried to run my program with executable and it runs without an error. I am posting my .c and .h files below, any help appreciated.
ReadFile1.c:
#include "ReadFile1.h"
#define MAX_STR_LEN 257
#define MAX_Color_Maps 17
int __declspec(dllexport) __stdcall ReadF(char* ColorMap)
{
FILE* bookFile;
/* allocation of the buffer for every line in the File */
char* buf = malloc(MAX_STR_LEN);
char* tmp;
/* if the space could not be allocated, return an error */
if (buf == NULL)
{
printf("No memory\n");
return 1;
}
if ((bookFile = fopen("Colormaps2.csv", "r")) == NULL) //Reading a file
{
printf("File could not be opened.\n");
printf("%s",strerror(errno));
return 1;
}
struct Color_decider Colors[MAX_Color_Maps];
int i = 1;
fgets(buf, 256, bookFile);
tmp = strtok(buf, ";");
char* temp1;
temp1= strdup(tmp);
strncpy(Colors[0].Color_maps, temp1, strlen(temp1));
while (i<17)
{
tmp = strtok(NULL, ";");
temp1 = strdup(tmp);
strncpy(Colors[i].Color_maps, temp1, strlen(temp1));
i++;
}
for (int k = 1; k < 17; k++)
{
if (!strcmp(Colors[k].Color_maps, ColorMap)) // Find the input column.
{
for (int j = 0; j < 256; j++)
{
fgets(buf, 256, bookFile);
tmp = strtok(buf, ";");
for (int l = 1; l < k * 3; l++)
tmp = strtok(NULL, ";");
tmp = strtok(NULL, ";");
temp1 = strdup(tmp);
Colors->C[j][0] = atoi(temp1);
tmp = strtok(NULL, ";");
temp1 = strdup(tmp);
Colors->C[j][1] = atoi(temp1);
tmp = strtok(NULL, ";");
temp1 = strdup(tmp);
Colors->C[j][2] = atoi(temp1);
printf("%d\t", Colors->C[j][0]);
printf("%d\t", Colors->C[j][1]);
printf("%d\n", Colors->C[j][2]);
}
break;
}
}
free(buf);
fclose(bookFile);
return 0;
}
ReadFile1.h
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
struct Color_decider {
char Color_maps[10];
int C[256][3];
};
char *strdup(char *org)
{
int org_size;
static char *dup;
char *dup_offset;
/* Allocate memory for duplicate */
org_size = strlen(org);
dup = (char *)malloc(sizeof(char)*org_size+1);
if( dup == NULL)
return( (char *)NULL);
/* Copy string */
dup_offset = dup;
while(*org)
{
*dup_offset = *org;
dup_offset++;
org++;
}
*dup_offset = '\0';
return(dup);
}
int __declspec(dllexport) __stdcall ReadF(char* ColorMap);