Mungkin file web.config Anda salah atau tidak memiliki beberapa tag. Saya memecahkan masalah saya menggunakan tag konfigurasi yang benar untuk .NET 4.
<system.web>
<compilation debug="true" strict="false" explicit="true" targetFramework="4.0">
<assemblies>
<add assembly="System.Deployment, 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.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
<add assembly="System.Data, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
<add assembly="System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
<add assembly="System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
<add assembly="System.Web.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
<add assembly="System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
<add assembly="System.Transactions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
</assemblies>
</compilation>
<pages controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID">
<namespaces>
<clear/>
<add namespace="System"/>
<add namespace="System.Collections"/>
<add namespace="System.Collections.Specialized"/>
<add namespace="System.Configuration"/>
<add namespace="System.Text"/>
<add namespace="System.Text.RegularExpressions"/>
<add namespace="System.Web"/>
<add namespace="System.Web.Caching"/>
<add namespace="System.Web.SessionState"/>
<add namespace="System.Web.Security"/>
<add namespace="System.Web.Profile"/>
<add namespace="System.Web.UI"/>
<add namespace="System.Web.UI.WebControls"/>
<add namespace="System.Web.UI.WebControls.WebParts"/>
<add namespace="System.Web.UI.HtmlControls"/>
</namespaces>
</pages>
<authentication mode="None"/>
</system.web>