The large number of ASP.old programmers migrating their code to ASP.NET ensures that error messages are one of the first things an ASP.NET programmer will typically see. Fortunately, not only is the debugging information provided by ASP.NET much better than ASP.old, but you have much more granular control over how debugging information is displayed in ASP.NET.
An ASP.NET debug page is displayed when an unhandled error is encountered, as long as the appropriate @Page or Web.config settings exist. The output of the page is composed of:
The application (or Web directory) where the error took place
The type of error and a description of the error
Details of the error from the compiler
Source code displaying where the error ...