C: Error munmap_chunk(): invalid pointer if to much data

Question

I found a lot of similar questions concerning this error, but the answers I found did not help me.

My program works for eleven data points which I read from a list "data.dat" without errors. If I increase the number of data points I get this error I don't understand. The file with my data consists of three columns of float numbers.

Here is a short version of my code.

    #define DIM 3

    #include <stdlib.h>
    #include <math.h>
    #include <stdio.h>
    #include <string.h>

    // Recursive function to build tree
    void my_function(FILE* outFile, double* r, int* idxList, unsigned long int* Nodes, int *node, int n, unsigned long int myKey)
    {
         unsigned long int myKey1 = myKey;

         for(int q=0; q<8; q++)
         {
              fprintf(outFile, "%d %d %d\n", q, n, *node);
              myKey1 = (myKey << 3)|q;
              Nodes[*node] = myKey1; 
              *node += 1;    
              if(*node < 20)
              {
                   my_function(outFile, r, idxList, Nodes, node, n, myKey1);
              }
         }
    }

    int main(int argv, char** argc)
    {
         FILE *inFile;
         inFile = fopen("data.dat", "r");

         FILE *outFile;
         outFile = fopen("result.dat", "w");

         unsigned int n = 15; // Number of points
         unsigned int N = n*DIM; // Elements in array

         // Array for points
         double *r = NULL;
         r = (double*)malloc(sizeof(double)*N);

         unsigned long int *Nodes = NULL;
         Nodes = (unsigned long int*)malloc(sizeof(unsigned long int)*3*n);
         for(int i=0; i<3*n; i++)
         {
              Nodes[i] = 0b0;
         }

         int *idxList = NULL;
         idxList = (int*)malloc(sizeof(int)*3*n);
         memset(idxList, -1, sizeof(int)*3*n); // Set all entries to -1

         for(int k=0; k<N; k++)
         {
              fscanf(inFile, "%lf", &r[k]);
         }

  int node = 0;
 unsigned long int myKey = 0b1;

         my_function(outFile, r, idxList, treeNodes, &node, n, myKey);

         // Close files
         fclose(inFile);
         fclose(outFile);

         // Clean up
         free(r);
         free(Nodes);
         free(idxList);
    }

The program works, but if I put more data points to the list, I get the following error.

*** Error in `./myProgram': munmap_chunk(): invalid pointer: 0x0000000000f74810 Aborted (core dumped)

If I comment the section

 // Close files
 fclose(inFile);
 fclose(outFile);

 // Clean up
 free(r);
 free(Nodes);
 free(idxList);

of my code, the error disappears. How can I fix this error? Any suggestions?