In the above code,it seems that [UIHint] is not applied properly. so get things work, kindly initialize the TinyMCE manualy, i mean change you code as ,
$("#ddl").change(function () {
var strSelected = "";
$("#ddl option:selected").each(function () {
strSelected += $(this)[0].value;
});
if (strSelected.length != 0) {
var url = "/Reseller/MailPartial/?resellerId=" + strSelected;
$("#mail").empty();
$("#mail").load(url);
**Re-Init TinyMCE**
InitTinyMCE();
}
function InitTinyMCE()
{
$('#@ViewData.TemplateInfo.GetFullHtmlFieldName(string.Empty)').tinymce({
// Location of TinyMCE script
script_url: '@Url.Content("~/Scripts/tinymce/tiny_mce.js")',
theme: "advanced",
height: "170",
width: "240",
verify_html : false,
plugins : "pagebreak,style,layer,table,save,advhr,advimage,advlink,emotions,iespell,inlinepopups,insertdatetime,preview,media,searchreplace,print,contextmenu,paste,directionality,fullscreen,noneditable,visualchars,nonbreaking,xhtmlxtras,template,wordcount,advlist,autosave",
// Theme options
theme_advanced_buttons1: "undo, redo,pasteword,|, bold, italic, underline,|,justifyleft,justifycenter,justifyright,justifyfull,|,image, emotions" ,
theme_advanced_buttons2: "charmap, bullist, numlist,|,formatselect,fontselect,fontsizeselectcode, |,tiny_mce_wiris_formulaEditor, fullscreen",
theme_advanced_buttons3: "",
theme_advanced_toolbar_location: "top",
theme_advanced_toolbar_align : "left",
theme_advanced_statusbar_location : "bottom",
theme_advanced_resizing : true,
// Example content CSS (should be your site CSS)
content_css : "@Url.Content("~/Scripts/tinymce/css/content.css")",
convert_urls : false,
// Drop lists for link/image/media/template dialogs
template_external_list_url : "lists/template_list.js",
external_link_list_url : "lists/link_list.js",
external_image_list_url : "lists/image_list.js",
media_external_list_url : "lists/media_list.js"
});
}