Originally Posted by
vmanes 
That error generally means that at some point your program wrote to a location outside the array's allocated memory. You see the error at the delete statement because the VS debugger gives these warnings at program exit.
Check your array access carefully for any out of bounds writing.
You were right. I checked the values of the array after the sort and I found a weird value (-3 billion ...). I used the provided heapsort in a wrong way.
Thanks for the help!