error checkbox

[davicito]

Porque me da error? :S

echo '<script language="javascript">
function changeColor(){
if(document.formdelete_vetercop.checkboxdelete_vet ercop_option.checked){
document.formdelete_vetercop.checkboxdelete_veterc op_option.style.background="#ec4848";
}else{
document.formdelete_vetercop.checkboxdelete_veterc op_option.style.background="#ffffff";
}
}
</script>';


while($list_vetercop_1=mysql_fetch_array($list_vet ercop)){
echo '<tr><form method=POST action=contratos.php?contrato=delete_vetercop_ok name=delete_vetercop><td>
<input name=delete_vetercop_option[] type=checkbox value='.$list_vetercop_1['codigo_vetercop'], onclick="changeColor()" >