Why does the name of a source file affect compilation?

I came across something really weird when I wrote a little lotto program in C++ called "lotto.cpp". Everything was fine until I wrote the write-to-file for my program. When I compiled, it showed me the following error:

ld: can't open output file for writing: lotto, errno=21 for architecture x86_64
collect2: ld returned 1 exit status

By coincidence, I changed the name of my program to "1.cpp", and all of a sudden it compiled without problems. It also worked when I changed the name to "test.cpp".

I am really curious as to why this happened. Any Ideas?

This happened on a MacBook Pro.

If you want the code as well, just let me know!

I know some people asked for the code. Here it is:

#include <iostream>
#include <fstream>

using namespace std;

const int NED  = 10;            
const int VIKING =  6;
const int NORMAL =  7;
const int MAX  = 10;

void quickSort(int arr[], int left, int right);
int checkDuplicates(int arr[], int length);

int main (int argc, const char *argv[])
{
    int i, j, k, ans;
    char ans2;
    int lottoNumbers[MAX];

    ofstream out("Lotto.txt", ios::out | ios::app);

    srand((unsigned)time(NULL));    

    do
    {
        do
        {
            cout << "\n\nDo you want to play Viking Lotto (press 6), or normal Lotto (press 7): ";
            cin >> ans;
        }while(ans != VIKING && ans != normal);

        (ans == VIKING) ? cout << "\nViking Lotto:\n" : cout << "\n\nnormal Lotto:\n";
        (ans == VIKING) ? out << "\nViking Lotto:\n" : out << "\n\nnormal Lotto:\n";


        for (i = 0; i < NED; i++)       //10 rows
        {       
            for (j = 0; j < ans; j++)  //6 or 7 columns
            {
                (ans == VIKING) ? lottoNumbers[j] = (rand() % 48) + 1 : lottoNumbers[j] = (rand() % 34) + 1;
            }
            if(checkDuplicates(lottoNumbers, ans) != -1)