调用DLL的有关问题

调用DLL的问题
小弟最近学习delphi中调用DLL，遇到一个问题：调用一个颜色对话框7次后出现如下错误"Project TestProject.exe raised exception class EAccessViolation with message 'Access violation at address 00383104' in module 'ColorProject.dll'.Read of address 69207021'.Process Stopped.Use Step or Run to continue."

下面贴出代码:
ColorUnit.pas:

unit ColorUnit;

interface
  uses Windows, Messages,SysUtils,Variants,Classes,Graphics,Controls,Forms,Dialogs,StdCtrls;
  function ColorValue():string;stdcall;
implementation
  function ColorValue():string;stdcall;
  var ColorDialog1:TColorDialog;
  begin
  ColorDialog1:=TColorDialog.Create(nil);
  ColorDialog1.Execute;
  ColorDialog1.Options:=ColorDialog1.Options+[cdAnyColor];
  result:='$'+InttoHex(ColorDialog1.Color,6);
  showmessage('$'+InttoHex(ColorDialog1.Color,6));
  ColorDialog1.Destroy;
  end;
end.
--------------------
ColorProject.dpr

library ColorProject;

{ Important note about DLL memory management: ShareMem must be the
  first unit in your library's USES clause AND your project's (select
  Project-View Source) USES clause if your DLL exports any procedures or
  functions that pass strings as parameters or function results. This
  applies to all strings passed to and from your DLL--even those that
  are nested in records and classes. ShareMem is the interface unit to
  the BORLNDMM.DLL shared memory manager, which must be deployed along
  with your DLL. To avoid using BORLNDMM.DLL, pass string information
  using PChar or ShortString parameters. }

uses
  Windows,Messages,SysUtils,Variants,Classes,Graphics,Controls,Forms,Dialogs,StdCtrls,ColorUnit in 'ColorUnit.pas';

{$R *.res}
  exports ColorValue;
begin
end.

----------------------------------------

TestUnit.pas

unit TestUnit;

interface

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

type
  TForm1 = class(TForm)
  Button1: TButton;
  procedure Button1Click(Sender: TObject);
  private
  { Private declarations }
  public
  { Public declarations }
  end;

var
  Form1: TForm1;

implementation
  function ColorValue():string;stdcall;
  External 'ColorProject.dll';
{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  ColorValue();
end;

end.

希望各位指点迷津啊。。。。。

[解决办法]
dll里的函数参数或返回类型都不要用string，换pchar
要么在uses第一个加上sharemem
[解决办法]

Delphi(Pascal) code

{ Important note about DLL memory management: ShareMem must be the  first unit in your library's USES clause AND your project's (select  Project-View Source) USES clause if your DLL exports any procedures or  functions that pass strings as parameters or function results. This  applies to all strings passed to and from your DLL--even those that  are nested in records and classes. ShareMem is the interface unit to  the BORLNDMM.DLL shared memory manager, which must be deployed along  with your DLL. To avoid using BORLNDMM.DLL, pass string information  using PChar or ShortString parameters. }
[解决办法]
简单点
dll和exe工程最先引用ShareMem  
Delphi(Pascal) code
uses  ShareMem, Windows,Messages,SysUtils...