Internal server error, was working good before, suddenly error! please help!

Hello, i have a .net website that was working fine previously. Suddenly i get an internal server error, with no more information displayed although i have unchecked "show friendly error". I contacted the hosting company and they said that there is an error in the web.config file, and they gave me this

error:

Module CustomErrorModule Notification SendResponse Handler PageHandlerFactory-Integrated Error Code 0x80070021 Config Error This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false". Config File \\?\D:\hshome\"path to site"\web.config

I have read about the internal error on several sites and tried adding handlers and overridemodes and what not, but it is still not working. Can someone PLEASE help me? And is it not strange that it suddently shows an error, without any files being changed? The site was working perfectly earlier.
This is my web.config file:

" Asp.Net Configuration option in Visual Studio. A full list of settings and comments can be found in machine.config.comments usually located in \Windows\Microsoft.Net\Framework\v2.x\Config --> --> --> section enables configuration of the security authentication mode used by ASP.NET to identify an incoming user. --> section enables configuration of what to do if/when an unhandled error occurs during the execution of a request. Specifically, it enables developers to configure html error pages to be displayed in place of a error stack trace. --> "

<?xml version="1.0"?>
<!--
Note: As an alternative to hand editing this file you can use the
web admin tool to configure settings for your application. Use
the Website->Asp.Net Configuration option in Visual Studio.
A full list of settings and comments can be found in
machine.config.comments usually located in
\Windows\Microsoft.Net\Framework\v2.x\Config
-->
<configuration>
<configSections>
<section name="SecurePages" type="System.Configuration.NameValueFileSectionHandler, System, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
</configSections>
<SecurePages>
<add key="/administrator" value="directory" />
<!--<add key="/images" value="directory" />-->
<add key="/BullCart.master" value="page" />
<add key="/ShoppingCart.aspx" value="page" />
<add key="/ForgotPassword.aspx" value="page" />
<add key="/Response.aspx" value="page" />
<!--<add key="/WebResource.axd" value="page" />-->
</SecurePages>
<system.net>
<mailSettings>
<smtp>
<network host="removed info" />
</smtp>
</mailSettings>
</system.net>
<appSettings>
<add key="senstitive info" />

<add key="FromEmail" value="" />
<add key="APIKey" value="" />
<add key="Secret" value="" />
<add key="CancelPurchaseUrl" value="" />
<add key="ReturnUrl" value="" />
<add key="NotifyUrl" value="" />
<add key="Sandbox" value="false" />
<add key="SendToReturnURL" value="false" />
<!-- PayPal Website Payment Pro Parameters-->
<add key="UseSandbox" value="false" />
<add key="Username" value="" />
<add key="Password" value="" />
<add key="Signature" value="" />
<!-- Captcha Code Parameters -->
<add key="RefreshDataSetEvery" value="3" />
<add key="UseToStore" value="IpAddress" />
</appSettings>
<connectionStrings>
<add name=*sensitive information* />

</connectionStrings>
<system.web>
<!--
Set compilation debug="true" to insert debugging
symbols into the compiled page. Because this
affects performance, set this value to true only
during development.
-->
<compilation debug="true" targetFramework="4.0">
<assemblies>
<add assembly="System.Web.Extensions.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
<add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
<add assembly="System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
<add assembly="System.Security, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
</assemblies>
<buildProviders>
<add extension=".edmx" type="System.Data.Entity.Design.AspNet.EntityDesignerBuildProvider" />
</buildProviders>
</compilation>
<!--
The <authentication> section enables configuration
of the security authentication mode used by
ASP.NET to identify an incoming user.
-->
<!--
The <customErrors> section enables configuration
of what to do if/when an unhandled error occurs
during the execution of a request. Specifically,
it enables developers to configure html error pages
to be displayed in place of a error stack trace.
-->
<customErrors mode="off" />
<anonymousIdentification enabled="true" />
<profile enabled="true" defaultProvider="SqlProvider">
</profile>
<pages controlRenderingCompatibilityVersion="4.0" clientIDMode="AutoID" />
</system.web>
<!--
The system.webServer section is required for running ASP.NET AJAX under Internet
Information Services 7.0. It is not necessary for previous version of IIS.
-->
<system.webServer>
<httpErrors errorMode="Detailed" />
</system.webServer>
</configuration>

Plese someone help me!
Thanks!

Moved from the asp forum

Have you tried look at this BLOG ?