When using VS2003 and 2005, when debugging by F5 (start), the following error message appears:

The web application you are trying to access on this web server is currently unavailable. Please click on the "Refresh" button in your web browser to retry your request.

Administrator Considerations: An error message detailing the reason for this particular request failure can be found in the system event log of the web server. Please check this log entry to find out what caused the error to occur.

And there was a server error when I first entered VS.

Server introduction

A server is a piece of computer software that manages resources and provides services to users. It is usually divided into file servers, database servers, and application servers. A computer or computer system running the above software is also referred to as a server. Compared with ordinary PCs, servers require higher stability, security, performance, etc., so CPU, chipset, memory, disk system, network and other hardware are different from ordinary PCs.

From these aspects, it can be measured whether the server has achieved its design purpose; R: Reliability reliability; A: Availability availability; S: Scalability scalability; U: Usability ease of use; M: Manageability manageability, ie server The RASUM metric.