Please try to add this code to your page.
<script>
$.map(['validatebox','textbox','passwordbox','filebox','searchbox',
'combo','combobox','combogrid','combotree',
'datebox','datetimebox','numberbox',
'spinner','numberspinner','timespinner','datetimespinner'], function(plugin){
if ($.fn[plugin]){
$.fn[plugin].defaults.missingMessage = 'This field is required.';
}
});
if ($.fn.validatebox){
$.fn.validatebox.defaults.rules.email.message = 'Please enter a valid email address.';
$.fn.validatebox.defaults.rules.url.message = 'Please enter a valid URL.';
$.fn.validatebox.defaults.rules.length.message = 'Please enter a value between {0} and {1}.';
$.fn.validatebox.defaults.rules.remote.message = 'Please fix this field.';
}
</script>