I need help with a custom form validation script

[moonchild]

I'm not very good at javascript at all, I haven't even touched it in forever. I am trying to write this function to validate my form, return an error or submit it, but it gives me the following error:

Error: 'manditory_fields' is null or is not an object.

This happens when I click submit on my form (the submit button is calling this function via onClick).

Here is the code:

<script language="JavaScript" type="text/javascript">
<!--

function check_logon_form(name)
{
	var manditory_fields = new Array("username","password","access_code");
	var error_fields = new Array();
	var i;
	var j;
	var k = 1;
	var err_str;
	var obj = document.forms[name];

	for ( i = 0; i <= manditory_fields.length; i++ )
	{
		var field = obj.manditory_fields[i].value;
		if ( field == '' )
		{
			error_fields[i] = manditory_fields[i];
		}
	}

	if ( error_fields.length > 0 )
	{
		err_str = '<b>The following errors occurred:</b><br />';
		for ( j = 0; j <= error_fields.length; j++ )
		{
			err_str += '- ' + error_fields[j];
			if ( k < error_fields.length )
			{
				err_str += '<br />';
			}
		k++;
		}
		document.error_msg.InnerHTML = err_str;
	}
	else
	{
		obj.submit();
	}
}

//-->
<script>