USBD_Initialize return usbThreadError

hi, Tsuneo, i found some code, but i don't know why memory pool is smaller than size? the last line, return NULL

void *rt_alloc_mem (void *pool, U32 size) {
  MEMP *p, *p_search, *p_new;
  U32   hole_size;

  if ((pool == NULL) || (size == 0)) return NULL;

  /* Add header offset to 'size' */
  size += sizeof(MEMP);
  /* Make sure that block is 4-byte aligned  */
  size = (size + 3) & ~3;

  p_search = (MEMP *)pool;
  while (1) {
    hole_size  = (U32)p_search->next - (U32)p_search;
    hole_size -= p_search->len;
    /* Check if hole size is big enough */
    if (hole_size >= size) break;
    p_search = p_search->next;
    if (p_search->next == NULL) {
      /* Failed, we are at the end of the list */
      return NULL;
    }
  }

i copied the usb HID (MCBSTM32E) example and test, but the result is same.

Hi:
can you describe your system a bit more:
- what microcontroller are you using?
- are you using Keil board (and if so which one)?

In RTX_Conf_CM.c, i turned main thread and default thread stack size to 400, the problem solved.
i am using stm32f103ze chip, not keil board.