Okay, I got this working now.

Code:
function callItemMenue()
{
	VECTOR temp;
	vec_set(temp,entPlayer.x);
	vec_to_screen(temp, camera);
	
	MENU* ringMenue = createMenue(temp.x, temp.y, 64, 64);
	ringMenue->cancel_id = MI_ID_CALL_MAINMENUE;
	
	int i;
	for (i = 0; i < inventoryGetCount(inventoryItem); i += 1)
	{
		ITEM_DATA* itData = inventoryGetItemData(inventoryItem, i);
		
		MENU_ITEM* it = createMenuItem(itData->name, itData->desc, itData->icon);
		it->kind = MI_KIND_ITEM;
		it->dec_id = inventoryItem->item_id[i];
		addMenueItem(ringMenue, it);
		
		sys_marker("ITD");
		//ptr_remove(itData);
		sys_marker(NULL);
	}
	showMenue(ringMenue);
	
	return (ringMenue);
}



The error was "ptr_remove(itData)" which must be sys_free(itData), because itData is no engine-object but a user defined struct...

That caused the crash.