C#

<br />
[DllImport("Netapi32.dll")]<br />
    extern static int NetLocalGroupAddMembers(<br />
      [MarshalAs(UnmanagedType.LPWStr)] string servername,<br />
      [MarshalAs(UnmanagedType.LPWStr)] string groupname,<br />
      int level,<br />
      ref LOCALGROUP_MEMBERS_INFO_3[] buf,<br />
      int totalentries<br />
    );<br />
<br />
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]<br />
    public struct LOCALGROUP_MEMBERS_INFO_3<br />
    {<br />
      public string domainandname;<br />
    }<br />
<br />
private enum NERR_GROUP_MEMBER_ADD<br />
    {<br />
      NERR_Success = 0,<br />
<br />
      // The local group specified by the groupname parameter does not exist.  <br />
      NERR_GroupNotFound = 1,<br />
<br />
      // The user does not have access to the requested information.    <br />
      ERROR_ACCESS_DENIED = 2,<br />
<br />
      // One or more of the members specified <br />
      // do not exist. Therefore, no new members were added.<br />
      ERROR_NO_SUCH_MEMBER = 3,<br />
<br />
      // One or more of the members specified were already <br />
      // members of the local group. No new members were added.<br />
      ERROR_MEMBER_IN_ALIAS = 4,<br />
<br />
      // One or more of the members cannot be added because their <br />
      // account type is invalid. No new members were added.<br />
      ERROR_INVALID_MEMBER = 5<br />
    }<br />

<br />
public bool NetLocalGroupAddMember(string groupname, string username)<br />
    {      <br />
      LOCALGROUP_MEMBERS_INFO_3 member = new LOCALGROUP_MEMBERS_INFO_3();<br />
      member.domainandname = Environment.UserDomainName + @"\" + username;<br />
<br />
      LOCALGROUP_MEMBERS_INFO_3[] members = new LOCALGROUP_MEMBERS_INFO_3[] { member };<br />
      <br />
      int retVal = NetLocalGroupAddMembers(SERVER_NAME, UserManager.DEFAULT_GROUPNAME, 3, ref members, 1);<br />
<br />
      if (retVal != (int)NERR_GROUP_MEMBER_ADD.NERR_Success)<br />
      {<br />
        MessageBox.Show("Error Adding Member to Group",<br />
         "Error",<br />
         MessageBoxButtons.OK,<br />
         MessageBoxIcon.Error);<br />
         return false;<br />
      }<br />
      return true;<br />
    }<br />

<br />
NET_API_STATUS NetLocalGroupAddMembers(<br />
  LPCWSTR servername,<br />
  LPCWSTR groupname,<br />
  DWORD level,<br />
  LPBYTE buf,<br />
  DWORD totalentries<br />
);<br />