Почитай описаловку, там что-то поменялось со времен XP
https://msdn.microsoft.com/ru-ru/library/windows/desktop/aa366358(v=vs.85).aspx On Windows Vista and later, a NULL pointer passed as the pMacAddr or PhyAddrLen parameter to the SendARP function causes an access violation and the application is terminated. If an error occurs on Windows Vista and later and ERROR_BAD_NET_NAME, ERROR_BUFFER_OVERFLOW, or ERROR_NOT_FOUND is returned, the ULONG value pointed to by the PhyAddrLen parameter is set to zero. If the ULONG value pointed to by the PhyAddrLen parameter is less than 6 on Windows Vista and later, SendARP function returns ERROR_BUFFER_OVERFLOW indicating the buffer to receive the physical address is too small. If the SrcIp parameter specifies an IPv4 address that is not an interface on the local computer, the SendARP function on Windows Vista and later returns ERROR_NOT_FOUND.