When I Run Below Code I Faced TypeError: r.innerText is undefined.

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PHP

Hello Everyone.

I Faced One Error,which can't solved by myself. I Have Searched a lot about it.
But Can't Find Solution. Please Help to Solve this bug.

Thanks In Advance.
Viral

Here's My Code.

<?php require "_header.php" ?>

<script language="javascript" type="text/javascript">

Ext.onReady(function(){
	
	  var demoform = new Ext.FormPanel({
		  
		      id:'demoform',
			  url:'save_demo2.php',
			  method:'post',
			  autoHeight:true,
			  frame:true,
			  layout:'form',
			  labelWidth:100,
			  items:[{
				        columnWidth:1,
						xtype:'fieldset',
					    items:[
						     {
							     xtype:'hidden',
								 id:'id',
								 name:'id',
								 hidden:true	 
							 } 
							 ,
							 {
						          xtype:'textfield',
								  fieldLabel:'Firstname',
								  id:'Firstname',
								  name:'Firstname',
								  allowBlank:'false'	     
							},
							{
							      xtype:'textfield',
								  fieldLabel:'Lastname',
								  id:'Lastname',
								  name:'Lastname',
								  allowBlank:false	
							},
							{
							      xtype:'textfield',
								  fieldLabel:'Address',
								  id:'Address',
								  name:'Address',
								  allowBlank:false	
							},
							{
							      xtype:'datefield',
								  fieldLabel:'Birthdate',
								  id:'Birthdate',
								  name:'Birthdate',
								  allowBlank:false	
							},
							{
							      xtype:'numberfield',
								  fieldLabel:'Mobile Number',
								  id:'Mobilenumber',
								  name:'Mobilenumber',
								  allowBlank:false	
							},
							{
							     xtype:'datefield',
								 fieldLabel:'Join Date',
								 id:'Joindate',
								 name:'Joindate',
								 allowBlank:false	
							}
							,
							{
							     xtype:'numberfield',
								 fieldLabel:'Salary',
								 id:'Salary',
								 name:'Salary',
								 allowBlank:false
								 	
							}]
				  }]
		 });
var demowindow = new Ext.Window({
		       title:'Registration',
			   autoHeight:true,
			   width:500,
			   items:demoform,
			   buttons:[{
				      text:'Register',
					  iconCls:'icon-save',
					  handler:function()
					  {
						  demoform.getForm().submit({
							  waitMsg:'Saving......'
						});  
					  }
				  }]
			});
	  var varwidth = (screen.width - demowindow.width)/2;
	  demowindow.show();
	});
</script>
<?php require "_footer.php" ?>