Why when I allocated staticly globaly memory like this
char a[10005][10005] = {0};
char d[10005][10005] = {0};
I got MLE 4, but not MLE 1?

You can used only:
char a[901][8101];
char d[901][8101];
Because 9....9 (100 times) S = 900 and S^2 = 8100

Maybe because of the compiler's optimizations