I have updated Telerik to the newest version (2017.1.228.40) and now the skin (Windows7) of the RadProgressBar seems broken (see attachement).
Code:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="ProgressBar.Default" %><%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik.Web.UI" TagPrefix="telerik" %><!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml"><head runat="server">    <title></title></head><body>    <form id="form1" runat="server">        <telerik:RadScriptManager ID="radScriptManager" runat="server" />        <div>            ProgressBar with default skin            <telerik:RadProgressBar ID="radProgressBar1" runat="server" BarType="Percent" Value="65" /><br /><br />            ProgressBar with Windows7 skin            <telerik:RadProgressBar ID="radProgressBar2" runat="server" BarType="Percent" Value="65" Skin="Windows7" /><br /><br />            Button with Windows7 skin            <telerik:RadButton ID="radButton" runat="server" Text="Button with Windows7 skin" Skin="Windows7" />        </div>    </form></body></html>