Document Object Is Not Set In Internet Explorer - Works In Firefox

I have a script that works in Firefox but not IE6-

<script language="JavaScript" type="text/javascript">
document.Params.ThisPageURL.value=document.URL;
var x = new Date ();
document.Params.TimeZoneOffset.value =x.getTimezoneOffset();
document.Params.submit ();
</script>

The form is set this way:
<FORM ACTION="<?php echo("$Action"); ?>" METHOD="POST" NAME="Params"
<input type="hidden" NAME="ThisPageURL" value=""><input type="hidden"
Name="$ERR" value=""><input type="hidden" name ="TimeZoneOffset"
value=""><input type="hidden" Name="$U" value=""><input type="hidden"
Name="$R" value=""><input type="hidden" Name="$T" value="">

I get the following error in IE:
document.Params.ThisPageURL is null or not an object

Any idea what the problem is ?