为什么我调用不了function里面的add()函数，如果去掉form就可以？

代码如下：
<html>
<head>
<title>生成试卷</title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<script language="javascript">
function add(){
var sum = 0;
var Add_sel = parseInt(add_sel.value);
if (!isNaN(Add_sel)){
sum += Add_sel;
}
var Add_blk = parseInt(add_blk.value);
if (!isNaN(Add_blk)){
     sum += Add_blk;
}
var Add_jud = parseInt(add_jud.value);
if (!isNaN(Add_jud)){
sum += Add_jud;
}
var Add_ans = parseInt(add_ans.value);
if (Add_ans){
sum += Add_ans;
}
var Add_aly = parseInt(add_aly.value);
if (Add_aly){
sum += Add_aly;
}
var Add_blief = parseInt(add_blief.value);
if (Add_blief){
sum += Add_blief;
}
add_all.value = sum;
}
function chkinput(form){
if (form.count.value==""){
alert("请输入题目总数！");
return false;
}
if (form.paperid.value==""){
alert("请输入试卷编号！");
return false;
}
}</script>
<style type="text/css">
<!--
body,td,th {
font-size: 14px;
}
-->
</style></head>
<body>
<form name="make_papers" action="" method="post" onSubmit="return chkinput(this)" >
  <table width="600">
    <tr align="center">
      <td width="110"  bgcolor="#CCFFFF">试卷题目总数</td>
      <td><input type="text" name="count" maxlength="6" size="5"
      onChange="if(/\D/.test(this.value)){alert('只能输入数字');this.value='';}"></td>
      <td width="80" bgcolor="#CCFFFF" >试卷编号</td>
      <td><input type="text" name="paperid" maxlength="6" size="5"
      onkeyup="value=value.replace(/[\W]/g,'')"
  onbeforepaste="clipboardData.setData('text',clipboardData.getData('text').replace(/[^\d]/g,''))">   </td>
    </tr>
    <tr align="center">
      <td rowspan="2"  bgcolor="#CCFFFF" width="60">题型</td>
      <td rowspan="2" bgcolor="#CCFFFF" width="80" > 题目总数</td>
      <td colspan="3" bgcolor="#CCFFFF">试题难易分配</td>
    </tr>
    <tr align="center">
      <td  bgcolor="#CCFFFF">难</td>
      <td  bgcolor="#CCFFFF">中</td>
      <td  bgcolor="#CCFFFF">易</td>
  <td  bgcolor="#CCFFFF">每道题总分</td>
    </tr>
    <tr align="center">
      <td bgcolor="#CCFFFF" >选择题</td>
      <td><input type="text" name="sel_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"></td>
      <td><input type="text" name="hard_count2" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"></td>
      <td><input type="text" name="center_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"></td>
      <td><input type="text" name="easy_count2" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"> </td>
  <td><input type="text" name="add_sel" size="5" onkeyup="add()"></td>
    </tr> 
    <tr align="center">
      <td bgcolor="#CCFFFF" >填空题</td>
      <td><input type="text" name="blk_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"></td>
      <td><input type="text" name="blk_h_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"></td>
      <td><input type="text" name="blk_c_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"></td>
      <td><input type="text" name="blk_e_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')"></td>
   <td><input type="text" name="add_blk" size="5" onkeyup="add()" ></td>
    </tr>
<tr align="center">
      <td bgcolor="#CCFFFF" >判断题</td>
      <td>
  <input type="text" name="jud_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">
  </td>
      <td><input type="text" name="jud_h_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">
  </td>
      <td><input type="text" name="jud_c_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">   
  </td>
      <td><input type="text" name="jud_e_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">  
  </td>
  <td><input type="text" name="add_jud" size="5" onkeyup="add()">    
  </td>
    </tr>
<tr align="center">
      <td bgcolor="#CCFFFF" >简答题</td>  
      <td><input type="text" name="ans_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">  
  </td>
      <td><input type="text" name="ans_h_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">
  </td>
      <td><input type="text" name="ans_c_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">  
  </td>
      <td><input type="text" name="ans_e_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">  
  </td>
  <td><input type="text" name="add_ans" size="5" onkeyup="add()"></td>
    </tr>
<tr align="center">
      <td bgcolor="#CCFFFF">分析题</td>
      <td><input type="text" name="aly_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">  
  </td>
      <td><input type="text" name="aly_h_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">  
  </td>
      <td><input type="text" name="aly_c_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">
  </td>
      <td><input type="text" name="aly_e_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">
  </td>
  <td><input type="text" name="add_aly" size="5" onkeyup="add()">   
  </td>
    </tr>
<tr align="center">
      <td bgcolor="#CCFFFF" >简述题</td>  
      <td><input type="text" name="blief_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">
  </td>
      <td><input type="text" name="blief_h_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">  
  </td>
      <td><input type="text" name="blief_c_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">   
  </td>
      <td><input type="text" name="blief_e_count" size="5"
      onkeyup="this.value=this.value.replace(/\D/g,'')"
      onafterpaste="this.value=this.value.replace(/\D/g,'')">   
  </td>
  <td><input type="text" name="add_blief"  size="5" onkeyup="add()"></td>
    </tr>
<tr>
      <td bgcolor="#CCFFFF" colspan="5" align="right">试卷总分</td>
      <td align="center">
  <input type="text" name="add_all"  size="5" onkeyup="add()">  
  </td>
    </tr>
    <tr align="center">
     <td colspan="6"><input type="submit" value="提交" name="make_paper"></td>
    </tr>
  </table>
</form>
</body>
</html>
请高手指点，谢谢！