Problem To execute javascript in presence of php

[sandipan.rcciit]

hi frnd,

i have a html form with some text fields and i have a check box that when i click on it the data form 1st text box come to the next one.

its working fine when i write the text in text box.
but if i use php value to the 1st text box retrived from database
the javascript gives an error that object expected.

i give my code here:

<?php
session_start();
$sid=$_SESSION['sid'];
$xyz=$_SESSION['username'];
include 'mysql-connect.php';
$sql=mysql_query("SELECT fullname FROM user_info WHERE username='$xyz'");
$r=mysql_fetch_array($sql);
$fullname=$r['fullname'];
echo $fullname;

$sql1=mysql_query("SELECT * FROM seller_acc_info WHERE username='$xyz'");
$n=mysql_num_rows($sql1);
if($n==0)
{
?>
/*ITS WORKING*/
<script language="JavaScript" type="text/javascript" src="checkout.js"></script>
<form action="abc.php" method="post" name="frmCheckout" id="frmCheckout" onSubmit="return checkShippingAndPaymentInfo();">
    <table width="550" border="0" align="center" cellpadding="5" cellspacing="1" class="entryTable">
        <tr class="entryTableHeader"> 
            <td colspan="2">Billing Information</td>
        </tr>
        <tr> 
            <td width="150" class="label">Full Name</td>
            <td class="content"><input name="txtShippingFirstName" type="text" class="box" id="txtShippingFirstName" size="30" maxlength="50"></td>
        </tr>
        
        
    </table>
    <p>&nbsp;</p>
    <table width="550" border="0" align="center" cellpadding="5" cellspacing="1" class="entryTable">
        <tr class="entryTableHeader"> 
            <td width="150">Payment Information</td>
            <td><input type="checkbox" name="chkSame" id="chkSame" value="checkbox" onClick="setPaymentInfo(this.checked);"> 
                <label for="chkSame" style="cursor:pointer">Same as Billing information</label></td>
        </tr>
        <tr> 
            <td width="150" class="label">Full Name</td>
            <td class="content"><input name="txtPaymentFirstName" type="text" class="box" id="txtPaymentFirstName" size="30" maxlength="50"></td>
        </tr>
        
        
    </table>
    <p>&nbsp;</p>
    
        <input class="box" name="btnStep1" type="submit" id="btnStep1" value="Proceed &gt;&gt;">
</form>
<?php
}
else
{
?>
/*ITS NOT WORKING*/
<form action="abc.php" method="post" name="frmCheckout" id="frmCheckout" onSubmit="return checkShippingAndPaymentInfo();">
    <table width="550" border="0" align="center" cellpadding="5" cellspacing="1" class="entryTable">
        <tr class="entryTableHeader"> 
            <td colspan="2">Billing Information</td>
        </tr>
        <tr> 
            <td width="150" class="label">Full Name</td>
            <td class="content"><input name="txtShippingFirstName" type="text" class="box" id="txtShippingFirstName" size="30" maxlength="50" value="<?php echo $fullname; ?>"></td>
        </tr>
        
        
    </table>
    <p>&nbsp;</p>
    <table width="550" border="0" align="center" cellpadding="5" cellspacing="1" class="entryTable">
        <tr class="entryTableHeader"> 
            <td width="150">Payment Information</td>
            <td><input type="checkbox" name="chkSame" id="chkSame" value="checkbox" onClick="setPaymentInfo(this.checked);"> 
                <label for="chkSame" style="cursor:pointer">Same as Billing information</label></td>
        </tr>
        <tr> 
            <td width="150" class="label">Full Name</td>
            <td class="content"><input name="txtPaymentFirstName" type="text" class="box" id="txtPaymentFirstName" size="30" maxlength="50"</td>
        </tr>
        
        
    </table>
    
    <p align="center"> 
        <input class="box" name="btnStep1" type="submit" id="btnStep1" value="Proceed &gt;&gt;">
    </p>
</form>
<?php
}
?>

and my java script code is:

function setPaymentInfo(isChecked)
{
	with (window.document.frmCheckout) {
		if (isChecked) {
			
			txtPaymentFirstName.value   = txtShippingFirstName.value;
			
			
			
			txtPaymentFirstName.readOnly   = true;
					
		} else {
			
			
			txtPaymentFirstName.readOnly   = false;
						
		}
	}
}

plz help me i dont understand what the problem...
plz its make very big problem for me..
thanks