Assuming you still want the validation code to run, you can disable the alert by overwriting the piece of code that handles the validation error.

Try adding this code snippet to the custom code section of your form (see http://app.formassembly.com/pages/support/customization)

<script type="text/javascript">
wFORMS.behaviors.validation.onFail = function(b) { }
</script>


This disables the alert, but also the scroll to the first error. If your form is particularly long, you can preserve the scrolling by using this instead:


<script type="text/javascript">
wFORMS.behaviors.validation.onFail = function(b) {
for (var id in b.elementsInError) {
var elem = document.getElementById(id);
if(elem.scrollIntoView) {
elem.scrollIntoView();
} else {
location.hash="#"+id;
}
break;
}
}
</script>