EC_KEY_new_by_curve_name returns NULL

[Khuc, Chuong D.]

Hi,
I got a problem with
EC_KEY_new_by_curve_name: it always return NULL. Here is how I used it:
EC_KEY *eckey = EC_KEY_new_by_curve_name(NID_ecdsa_with_SHA256);
If(eckey == NULL)
{
 printf("ERROR: NULL ECKEY!\r\n");
}
Do you happen to know the reason?