.net调用delphi写的dll,出错误

错误类型：出错误尝试读取或写入受保护的内存。这通常指示其他内存已损坏。

C#源码
[DllImport("Base64.dll")]
public static extern string Base64ToStr(string Base64);

protected void Page_Load(object sender, EventArgs e)
{
Response.Write(Base64ToStr("YWRtaW4="));
}

delphi 源码unit Base;

interface

uses ShareMem,SysUtils, Classes;

// 将SourceSize长度的源Source编码为Base64字符串返回
function Base64Encode(const Source; SourceSize: Integer): string; overload;
// 将Source从StartPos开始的Size长度的内容源编码为Base64，写入流Dest。Size=0文件结束
procedure Base64Encode(Source, Dest: TStream; StartPos: Int64 = 0; Size: Int64 = 0); overload;
// 把字符串Str编码为Base64字符串返回
function StrToBase64(Str: string): string;stdcall;

// 按给定的编码源Source和长度Size计算并返回解码缓冲区实际所需长度
function Base64DecodeBufSize(const Source; Size: Integer): Integer;
// 将Base64编码字符串Source解码存放在Buf中，返回解码长度
function Base64Decode(const Source: string; var Buf): Integer; overload;
// 将Source从StartPos开始的Size长度的Base64编码内容解码，写入流Dest。Size=0文件结束
procedure Base64Decode(Source, Dest: TStream; StartPos: Int64 = 0; Size: Int64 = 0); overload;
// 把Base64字符串解码为字符串返回
function Base64ToStr(Base64: string): string;stdcall;

implementation

const
  Base64_Ch