SQL2005 System.Security.Permissions.FileIOPermissi

在vs2005下编写的存储过程代码如下：
using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Xml;
public partial class StoredProcedures
{
    [Microsoft.SqlServer.Server.SqlProcedure]
    public static void StoredProcedure1()
    {
        SqlConnection cnn = new SqlConnection("context connection=true");
        cnn.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = cnn;
        cmd.CommandText = "select * from UserTest for xml raw('pesron')";
        XmlReader xr = cmd.ExecuteXmlReader();
        DataSet ds = new DataSet();
        ds.ReadXml(xr);
        ds.WriteXml("d://wu.xml");
    }
};

在sql2005下执行该存储过程时，出现以下错误：
消息 6522，级别 16，状态 1，过程 StoredProcedure1，第 0 行
在执行用户定义例程或聚合 'StoredProcedure1' 期间出现 .NET Framework 错误:
System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
System.Security.SecurityException:
  at System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet)
  at System.Security.CodeAccessPermission.Demand()
  at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)
  at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)
  at System.Xml.XmlTextWriter..ctor(String filename, Encoding encoding)
  at System.Data.DataSet.WriteXml(String fileName, XmlWriteMode mode)
  at System.Data.DataSet.WriteXml(String fileName)
  at StoredProcedures.StoredProcedure1()
。
谢谢！