读取OleVariant参数内容，报错！

[shq_cpst]

在程序中导入了一个OCX控件，其中使用的参数为如下两个：
function receiveMessage(var NetID: Smallint; var NodeID: Smallint; var UnitID: Smallint;
MessageType: OleVariant): OleVariant;
function sendFinsCommand(NetID: Smallint; NodeID: Smallint; UnitID: Smallint;
Message: OleVariant): Integer; overload;

编写程序为：
unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, OleCtrls, DBOleCtl, FINSMSGCTLLib_TLB;

type
TForm1 = class(TForm)
fnsmsg1: TFinsMsg;
btn1: TButton;
edt1: TEdit;
procedure btn1Click(Sender: TObject);
procedure fnsmsg1Receive(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.btn1Click(Sender: TObject);
begin
fnsmsg1.sendFinsCommand(0,2,0,'0701');
end;

procedure TForm1.fnsmsg1Receive(Sender: TObject);
var
a,b,c:SmallInt;
messagefins:OleVariant;
s:string;
begin
a:=0;
b:=2;
c:=0;
s := fnsmsg1.receiveMessage(a,b,c,messagefins);
end;

end.

单击“btn1",程序执行，发送指令：fnsmsg1.sendFinsCommand(0,2,0,'0701');顺序执行。控件接收到指令后，开始自动运行fnsmsg1Receive函数，到 s := fnsmsg1.receiveMessage(a,b,c,messagefins);行，系统抛出如下错误：
Project Project1.exe raised exception class EOleException with message "Unsupported Variant Type on the Method argument".Process stopped.
我把messagefins变为String类型也是一样的。
请大神给出较为详细的分析，最好能给出点吗，谢谢！

[yct0605]

messagefins的值是多少，从代码上看，a,b,c都有赋值，messagefins没有赋值？

[yct0605]

试试 s := fnsmsg1.receiveMessage(0,2,0,'0701'); 可有错误！