求救！！这个小程序怎会报内存不足？

<html>
<head>
<title>资料</title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
</head>
<SCRIPT language="JavaScript" >
var mstr;mstr="1234567890111111115666228355527252525255252552265q2525";var timer1;function stop_scroll()
{ 
  if (event.keyCode == 13)
    clearInterval(timer1);
} function start_scroll(){ 
  var n,id,sjhm;
  n = mstr.length/11; 
  id = parseInt(Math.random()*n);
  sjhm = mstr.substr(id*11,11);
  form1.showtxt.value = sjhm;
  }
</SCRIPT>
<body background="" leftmargin="0" topmargin="0" onKeyDown="return stop_scroll()">
<form name="form1" method="post" action="">
  <table width="100%" border="0" align="center" cellpadding="0" cellspacing="0">
     <tr> 
      <td>&nbsp;</td>
      <td>&nbsp;</td>
      <td height="22" align="left" valign="middle"><font size="2" face="宋体">第三步：按Enter开始抽奖</font></td>
      <td height="22" align="center" valign="middle"> <div align="left"> 
          <input name="begin" type="button"  class="bt" id="begin" onClick="timer1=setInterval('start_scroll()',1000);" value=" 开 始 ">
        </div></td>
      <td>&nbsp;</td>
    </tr>
     <tr>
       <td>&nbsp;</td>
       <td>&nbsp;</td>
       <td height="22" align="left" valign="middle">  
   <input name="showtxt" type="text" id="showtxt"  maxlength="100"></td>
       <td height="22" align="center" valign="middle">&nbsp;</td>
       <td>&nbsp;</td>
     </tr>
        </table>
        
      </td>
    </tr>
  </table>
</form></body>
</html>