When you try to debug an ASP.NET application in Visual Studio.NET. you may receive the following debugging error.

Error while trying to run project: Unable to start debugging on the web server. The project is not configured to be debugged.

Following are reasons and solutions for this problems.

Possibility 1:

You are not a part of debugger group.

Solution

Local Users and Groups ->Users- > add yourself as a Debugger User (Also check if you are a VSDeveloper

Possibility 2:

You dont have execute permissions on your virtual folder.

Solution

Step 1: Control Panel -> Administrative Tools- >Internet Service Manager

Step 2: Default Web Site -> Right Click on your Project-> Properties->Execute Permissions -> Scripts and Executables

Possibility 3:

You have kept ASP.NET debugging unchecked.

Solution

In VS.NET IDE,

Right Click Project - >Properties->Configuration Properties ->Debugging-> Debuggers Enable Check the checkbox for ASP.NET Debugging

For more details about this problem,
INFO: Common Errors When You Debug ASP.NET Applications in Visual Studio .NET

To know how to debug client side scripts in Visual Basic .NET,
HOW TO: Debug Client-Side Script in Visual Basic .NET