[рони]

svp,
попробуйте заменить файл целиком на это

function hilite(field) {
     document.my_form.elements[field].style.backgroundColor = "#AEC6DE"
}

function testData() {
    if (document.my_form.elements["Name_user"].value == "") {
        alert("\n\u0412\u0432\u0435\u0434\u0438\u0442\u0435 \u0412\u0430\u0448\u0435 \u0438\u043c\u044f!\t\n");
        hilite("Name_user");
        document.my_form.elements["Name_user"].focus();
        return false
    }
    if (document.my_form.elements["E_mail"].value == "") {
        alert("\n\u0412\u0432\u0435\u0434\u0438\u0442\u0435 E-mail!\t\n");
        hilite("E_mail");
        document.my_form.elements["E_mail"].focus();
        return false
    }
    if (document.my_form.elements["Subject"].value == "") {
        alert("\n\u0412\u0432\u0435\u0434\u0438\u0442\u0435 \u0442\u0435\u043c\u0443 \u0441\u043e\u043e\u0431\u0449\u0435\u043d\u0438\u044f!\t\n");
        hilite("Subject");
        document.my_form.elements["Subject"].focus();
        return false
    }
    if (document.my_form.elements["Message"].value == "") {
        alert("\n\u0412\u0432\u0435\u0434\u0438\u0442\u0435 \u0412\u0430\u0448\u0435 \u0441\u043e\u043e\u0431\u0449\u0435\u043d\u0438\u0435!\t\n");
        hilite("Message");
        document.my_form.elements["Message"].focus();
        return false
    }
    if (document.my_form.elements["keystring"].value == "") {
        alert("\n\u0412\u0432\u0435\u0434\u0438\u0442\u0435 \u043f\u0440\u043e\u0432\u0435\u0440\u043e\u0447\u043d\u044b\u0439 \u043a\u043e\u0434!\t\n");
        hilite("keystring");
        document.my_form.elements["keystring"].focus();
        return false
    }
};