Visual Studio 2008 has a feature that lets you step through the source code of the .NET framework when you are debugging. This can come in handy when you are trying to, for example, inherit from asp.net server controls to customize them, or figure out why a class is not operating as expected. This is not a feature that you will want turned on all the time because it will be inconvenient when debugging to have almost all of your errors stop in a .NET source file. Such as a KeyNotFoundException stopping in the Dictionary class. So be aware that this also turns off the Enable Just My Code (Managed only) option. You may want to turn this back on for regular development. However, To access this feature follow the steps below.
- On the menu navigate to Tools -> Options
- In the tree on the left inside the Options dialog that appears, navigate to Debugging -> General
- Scroll down and check the option Enable .NET Framework source stepping
the screen shot below shows the sections in the Options dialog where you need to make changes