Script to copy values not working

I have the script below, it copies values from one field of the form to another (addresses) when a checkbox is checked, then if unchecked the previous values are restored.

For some reason its simply not working:


<SCRIPT LANGUAGE="JavaScript">
var ResCareOf = "";
var ResStr = "";
var ResApt = "";
var ResCity = "";
var ResState = "";
var ResZip = "";
var ResCntry = "";
var ResCntryIndex = 0;

function InitSaveVariables(form) {
ResCareOf = form.ResCareOf.value;
ResStr = form.ResStr.value;
ResApt = form.ResApt.value;
ResCity = form.ResCity.value;
ResState = form.ResState.value;
ResZip = form.ResZip.value;
ResCntryIndex = form.ResCntry.selectedIndex;
ResCntry = form.ResCntry[ResCntryIndex].value;

}

function MailingtoResidenceAddress(form) {
if (form.copy.checked) {
InitSaveVariables(form);
form.ResCareOf.value = form.MailCareOf.value;
form.ResStr.value = form.MailStr.value;
form.ResApt.value = form.MailApt.value;
form.ResCity.value = form.MailCity.value;
form.ResState.value = form.MailState.value;
form.ResZip.value = form.MailZip.value;
form.ResCntry.selectedIndex = form.MailCntry.selectedIndex;

}
else {
form.ResCareOf.value = ResCareOf;
form.ResStr.value = ResStr;
form.ResApt.value = ResApt;
form.ResCity.value = ResCity;
form.ResState.value = ResState;
form.ResZip.value = ResZip;      
form.ResCntry.selectedIndex = ResCntry;
   }
}
//  End -->
</script>

The checkbox code is:

<input name="copy" type="checkbox" id="copy" value=""/>

The form name is 'form1'  and the field names are correct in the script.
I am not sure what I may be missing.