I'm not sure what I'm doing wrong. I get a warning when I compile and an error after my program runs.
This is the warning I get:
myList2.cpp: In function ‘int main()’:
myList2.cpp:96: warning: deleting array ‘int score [6]’

And this is what shows after my program runs:
a.out(7023) malloc: *** error for object 0x7fff6bae4bf0: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
Abort trap: 6

And this is my code:

#include <string>
#include <iostream>
using namespace std;

double getAverage(int* score, int n)
{
    int sum = 0;
    int c = 0;
    for (c = 0; c < n; c++)
        sum += score[c];
    double average = double(sum) / n;
    return average;
}

int compare(const void* pa, const void* pb)
  {
  const int& a = *static_cast<const int*>(pa);
  const int& b = *static_cast<const int*>(pb);
  if (a < b) return -1; // negative if a<b
  if (a > b) return 1; // positive if a>b
  return 0; // 0 for tie
  }

bool hasAScore(int size,int score[])
{
    int d;
    for (d=0; d < size; d++)
    {
        if (score[d] >= 90)
        {
            cout << "At least one 'A' grade is present" << endl;
            return true;
        }
    }
    cout << "No A grades present" << endl;
    return false;
}
int main()
{ 
  // create empty list
  const int MAX_SCORES = 6;
  int nScores = 0;
  int score[MAX_SCORES];

  // user input for amount of scores
  int size;
  cout << "How many scores? ";
  cin >> size;
  cin.ignore(1000, 10);
  int* scoreOne = new int[size];

  // read and save the scores
  int i;
  int aScore;
  for (i = 0; i < size; i++)
  {
    cout << "Enter the number: ";
    cin >> aScore;
    cin.ignore(1000, 10);

    if (nScores < MAX_SCORES)
        score[nScores++] = aScore;
  } // for

  // find the max and min integers
  int max = score[0];
  int min = score[0];
  int b;
  for (b = 1; b < size; b++)
  {
    if (max < score[b]) max = score[b];
    if (min > score[b]) min = score[b];
  } // for

  qsort(score, nScores, sizeof(int), compare);

  // printing the values
  for (i = 0; i < size; i++)
    cout << score[i] << ' ';
    cout << endl;
    cout << "Maximum: " << max << endl;
    cout << "Minimum: " << min << endl;
    cout << "Average = " << getAverage(score,size) << endl;
    hasAScore(size,score);
  delete [] score;

  cout << "Press ENTER to continue..." << endl;
  cin.get();

  return 0;
}

you can not delete arrays or other objects that were not allocated with new. All you have to do is delete line 85 because its not needed.