Request is not available in this context

<system.web>

 <customErrors mode="Off" />

        <authentication mode="Forms">

            <forms loginUrl="~/home" timeout="" slidingExpiration="true" />

        </authentication>

        <pages asyncTimeout="" />

        <compilation targetFramework="4.5" />

        <httpRuntime targetFramework="4.5" maxRequestLength="" executionTimeout="" />

        <sessionState mode="StateServer" timeout="" cookieless="false" />

        <globalization requestEncoding="utf-8" responseEncoding="utf-8" fileEncoding="utf-8" culture="zh-cn" />

    </system.web>