pcap_open_live returns NULL

[MonsterreactioN]

const u_char* ProjectSniffer::GetPacket(char *Dev)
{
    pcap_t *handle;                 // Session handler 
    struct pcap_pkthdr header;      // Header (von pcap vordefiniert)
    char errbuf[PCAP_ERRBUF_SIZE];  // Fehlerausgabe 
    const u_char *packet;           // Das aktuelle Paket

    handle = pcap_open_live(Dev, BUFSIZ, 0, 0, errbuf);
    if (handle==NULL)
    {
        return NULL;
    }

    // Packet Sniffen 
    packet = pcap_next(handle, &header);

    return packet;

}

It's In a Qt Program, it runs fine in a C Programm