Magento :: Save Form data in session when error occurs in form submit

1. IN Your Controller Get the form data and save values in session:

$data = Mage::app()->getRequest()->getPost();
Mage::getSingleton('customer/session')->setPostedData($data);

2. Then in the form page get the session values:

<?php $data = Mage::getSingleton('customer/session')->getPostedData(true);

3. And in form for each fields set the values:

<input type="text" name="field_name" value="<?php echo (isset($data['field_name']) ? $data['field_name'] : '') ?>"