javascript中一个奇怪的问题

下列一段代码是在javascript中动态生成列表框,错误提示"group为空或不是对象",哪位高手能帮帮忙,非常感谢!!!
var groups=document.getElementById("StudentInstitute").options.length;
var i;
var group=new Array(groups+1);
for (i=0;i<=groups;i++)
{
            group[i]=new Array();
}
group[0][0]=new Option("==请选择==","1212"); 
<%  int v,j,num,k=0;
for (v=1;v<=collegeLength;v++){
%>
group[<%=v%>][0] = new Option("==请选择==","212"); 
<%
num=dep[v];  ///获取每个学院的专业数;
///System.out.println("num="+num);
for (j=1;j<=num;j++){%>
///System.out.println("Department="+departmentList.get(k).getDepartmentName());
group[<%=v%>][<%=j%>]=new Option("<%=departmentList.get(k).getDepartmentName()%>","<%=departmentList.get(k).getDepartmentId()%>");
<%
k=k+1;
}
}
%>
var p,q;
 function Redirect(x)
{
for (q=document.getElementById("StudentDepartment").options.length-1;q>0;q--)
{

     document.getElementById("StudentDepartment").options[q]=null;
  
    }
for (p=0;p<group[x].length;p++)
{
document.getElementById("StudentDepartment").options[p]=new Option(group[x]  [p].text,group[x][p].value);
}
document.getElementById("StudentDepartment").options[0].selected = true ;
}