This article explains the need for understanding the HTTP status codes. The IIS 6.0 helps to display the appropriate status code for the built in core website. Most HTTP status codes have three digits, for example, 401. Some status codes have three digits followed by a decimal point, and one or two more digits (for example, 300.12). In such a case, the number that follows the decimal point is called the sub status code.
The following is the Status Code Range and the respective Code Types.
400 Client Error
500 Server Error
Under each status code, there will be a sub status code and it will have its own description on the issue.