ISAPI 过滤器遇到的未知问题，真是晕死人。

开发环境DELPHI2010+UPDATE4。
Embarcadero Delphi 2010 Version 14.0.3593.25826 
Copyright  Embarcadero Technologies, Inc. All Rights Reserved.用以上环境开发了一个ISAPI 过滤器，给WIN2003 IIS6。
结果发现在服务器IIS6上ISAPI筛选器的状态是可用（绿色箭头）
而优先级显示未知。打开网页跟踪代码结果发现。
  GetFilterVersion 这个函数是被加载了的。但是就是进入不了  HttpFilterProc
我真是晕。
有没有高手遇到过这样的问题。能帮我分析一下吗？
Library CURL;uses
  SysUtils,
  ComObj,
  Windows;const
    HTTP_FILTER_MAJOR          = 1; { major version of this spec }
    HTTP_FILTER_MINOR          = 0; { minor version of this spec }
    SF_MAX_USERNAME            = 257;
    SF_MAX_PASSWORD            = 257;
    SF_MAX_FILTER_DESC_LEN     = 257;{ SF_STATUS_TYPE }
    SF_STATUS_TYPE                     = $8000000;  { base value }
    SF_STATUS_REQ_FINISHED             = SF_STATUS_TYPE;
    SF_STATUS_REQ_FINISHED_KEEP_CONN   = SF_STATUS_TYPE + 1;
    SF_STATUS_REQ_NEXT_NOTIFICATION    = SF_STATUS_TYPE + 2;
    SF_STATUS_REQ_HANDLED_NOTIFICATION = SF_STATUS_TYPE + 3;
    SF_STATUS_REQ_ERROR                = SF_STATUS_TYPE + 4;
    SF_STATUS_REQ_READ_NEXT            = SF_STATUS_TYPE + 5;    SF_NOTIFY_SECURE_PORT              = $00000001;
    SF_NOTIFY_NONSECURE_PORT           = $00000002;
    SF_NOTIFY_READ_RAW_DATA            = $00008000;
    SF_NOTIFY_PREPROC_HEADERS          = $00004000;
    SF_NOTIFY_AUTHENTICATION           = $00002000;
    SF_NOTIFY_URL_MAP                  = $00001000;
    SF_NOTIFY_SEND_RAW_DATA            = $00000400;
    SF_NOTIFY_LOG                      = $00000200;
    SF_NOTIFY_END_OF_NET_SESSION       = $00000100;    SF_NOTIFY_ORDER_HIGH               = $00080000;
    SF_NOTIFY_ORDER_MEDIUM             = $00040000;
    SF_NOTIFY_ORDER_LOW                = $00020000;
    SF_NOTIFY_ORDER_DEFAULT            = SF_NOTIFY_ORDER_HIGH;
    SF_NOTIFY_ORDER_MASK               = (SF_NOTIFY_ORDER_HIGH or SF_NOTIFY_ORDER_MEDIUM or SF_NOTIFY_ORDER_LOW);type
    PVOID = Pointer;
    LPVOID = Pointer;
    PCardinal = ^Cardinal;    SF_REQ_TYPE = (SF_REQ_SEND_RESPONSE_HEADER, SF_REQ_ADD_HEADERS_ON_DENIAL,
                   SF_REQ_SET_NEXT_READ_SIZE, SF_REQ_SET_PROXY_INFO);    Type
      TFuncPlaceHolder = POINTER;    THTTP_FILTER_CONTEXT = record
      cbSize             : DWORD;
      Revision           : DWORD;
      ServerContext      : PVOID;
      ulReserved         : DWORD;
      fIsSecurePort      : BOOL;
      pFilterContext     : PVOID;
      GetServerVariable  : TFuncPlaceHolder; {TGetServerVariable;}
      AddResponseHeaders : TFuncPlaceHolder; {TAddResponseHeaders;}
      WriteClient        : TFuncPlaceHolder; {TWriteClient;}
      AllocMem           : TFuncPlaceHolder; {TAllocMem;}
      ServerSupportFunc  : TFuncPlaceHolder; {TServerSupportFunc;}
    end;
    HTTP_FILTER_CONTEXT = THTTP_FILTER_CONTEXT;
    PHTTP_FILTER_CONTEXT = ^HTTP_FILTER_CONTEXT;    TGetServerVariable  = Function(var pfc          : THTTP_FILTER_CONTEXT;
                                       VariableName : PChar;
                                       Buffer       : LPVOID;
                                       BuffSize     : PCardinal) : BOOL;
                                       StdCall;    TAddResponseHeaders = Function(var pfc          : THTTP_FILTER_CONTEXT;
                                       Headers      : PChar;
                                       Reserved     : DWORD) : BOOL;
                                       StdCall;    TWriteClient        = Function(var pfc          : THTTP_FILTER_CONTEXT;
                                       Buffer       : LPVOID;
                                       dwBytes      : LPDWORD;
                                       Reserved     : DWORD) : BOOL;
                                       StdCall;    TAllocMem           = Procedure(var pfc         : THTTP_FILTER_CONTEXT;
                                        cbSize      : DWORD;
                                        dwReserved  : DWORD);    TServerSupportFunc = Function(var  pfc          : THTTP_FILTER_CONTEXT;
                                       sfReq        : SF_REQ_TYPE;
                                       pData        : PVOID;
                                       ul1          : DWORD;
                                       ul2          : DWORD) : BOOL;
                                       StdCall;    THTTP_FILTER_RAW_DATA = record
      pvInData   : PVOID;
      cbInData   : DWORD;
      cbInBuffer : DWORD;
      dwReserved : DWORD;
    end;
    HTTP_FILTER_RAW_DATA  = THTTP_FILTER_RAW_DATA;
    PHTTP_FILTER_RAW_DATA = ^HTTP_FILTER_RAW_DATA;    TGetHeader = Function(var pfc       : THTTP_FILTER_CONTEXT;
                              lpszName  : PChar;
                              lpvBuffer : LPVOID;
                              lpdwSize  : LPDWORD) : BOOL; StdCall;    TSetHeader = Function(var pfc : THTTP_FILTER_CONTEXT;
                              lpszName  : PChar;
                              lpszValue : PChar) : BOOL; StdCall;    TAddHeader = Function(var pfc : THTTP_FILTER_CONTEXT;
                              lpszName  : PChar;
                              lpszValue : PChar) : BOOL; StdCall;
    THTTP_FILTER_PREPROC_HEADERS = record
      GetHeader  : TGetHeader;
      SetHeader  : TSetHeader;
      AddHeader  : TAddHeader;
      dwReserved : DWORD;
    end;
    HTTP_FILTER_PREPROC_HEADERS  = THTTP_FILTER_PREPROC_HEADERS;
    PHTTP_FILTER_PREPROC_HEADERS = ^HTTP_FILTER_PREPROC_HEADERS;
    THTTP_FILTER_AUTHENT = record
      pszUser        : PChar;
      cbUserBuff     : DWORD;
      pszPassword    : PChar;
      cbPasswordBuff : DWORD;
    end;
    HTTP_FILTER_AUTHENT  = THTTP_FILTER_AUTHENT;
    PHTTP_FILTER_AUTHENT = ^HTTP_FILTER_AUTHENT;
    THTTP_FILTER_URL_MAP = record
      pszURL : PChar;
      pszPhysicalPath : PChar;
      cbPathBuff : DWORD;
    end;
    HTTP_FILTER_URL_MAP  = THTTP_FILTER_URL_MAP;
    PHTTP_FILTER_URL_MAP = ^HTTP_FILTER_URL_MAP;
    THTTP_FILTER_LOG = record
      pszClientHostName : PChar;
      pszClientUserName : PChar;
      pszServerName     : PChar;
      pszOperation      : PChar;
      pszTarget         : PChar;
      pszParameters     : PChar;
      dwHttpStatus      : DWORD;
      dwWin32Status     : DWORD;
    end;
    HTTP_FILTER_LOG  = THTTP_FILTER_LOG;
    PHTTP_FILTER_LOG = ^HTTP_FILTER_LOG;
    THTTP_FILTER_VERSION = record
      dwServerFilterVersion : DWORD;
      dwFilterVersion       : DWORD;
      lpszFilterDesc        : array [0..(SF_MAX_FILTER_DESC_LEN-1)] of Char;
      dwFlags               : DWORD;
    end;
    HTTP_FILTER_VERSION = THTTP_FILTER_VERSION;
    PHTTP_FILTER_VERSION = ^HTTP_FILTER_VERSION;
procedure LogInfo (aStr : PChar);
const
  LogFileName = 'd:\FilterLog.txt';
Var
  OutFile : TextFile;
begin
  AssignFile (OutFile, LogFileName);
  If FileExists (LogFileName) then Append (OutFile) else Rewrite(OutFile);
  Writeln (OutFile, aStr);
  CloseFile (OutFile);
end;
Function GetFilterVersion(var pVer : HTTP_FILTER_VERSION) : BOOL; export; stdcall;
begin
  LogInfo('1111');
  try
    pVer.dwFilterVersion := MAKELONG(0, 1);
    StrPCopy(pVer.lpszFilterDesc, 'FanURL ReWrite - ISAPI Filter');
    pVer.dwFlags := (SF_NOTIFY_SECURE_PORT or SF_NOTIFY_NONSECURE_PORT or
                      SF_NOTIFY_PREPROC_HEADERS
                      or SF_NOTIFY_ORDER_DEFAULT);    result := True;
    LogInfo('2222');
  except
    result := False;
  end;
end;
Function HttpFilterProc(var pfc : HTTP_FILTER_CONTEXT;
                        NotificationType : DWORD;
                        pvNotification : LPVOID) : DWORD; export; stdcall;
begin
   LogInfo('3333');
   result :=0;
end;exports
  HttpFilterProc,
  GetFilterVersion;end.
日志文件中只生成了：
1111
2222
但是接下来的调用，HttpFilterProc并没有执行。3333不被记录。