Symptoms
This article describes how to enable the Option Strict and Option Explicit statements in Microsoft Visual Basic applications for code-behind files and files that are contained in the App_Code folder.
Resolution
To enable the Option Strict and Option Explicit statements in the code-behind files and files that are contained in the App_Code folder of a Visual Basic application, override the compiler configuration in the system.codedom section of the Web.config file for the application. To do this, add the following code to the Web.config file:

<system.codedom> <compilers> <compiler language=”c#;cs;csharp” extension=”.cs” type=”Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ warningLevel=”0″/> <compiler language=”vb;vbs;visualbasic;vbscript” extension=”.vb” type=”Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ warningLevel=”0″ /> </compilers> </system.codedom>