Run and install ASP through CMD prompt.(IIS error 500.21 solved)

This issue can be resolved by using one of the following method:

Method 1: Enable the Directory Browsing feature in IIS (Recommended)

To resolve this problem, follow these steps:

1. Start IIS Manager. To do this, click Start, click Run, type inetmgr.exe, and then click OK.
2. In IIS Manager, expand server name, expand Web sites, and then click the website that you want to modify.
3. In the Features view, double-click Directory Browsing.
4. In the Actions pane, click Enable.

Method 2: Add a default document

To resolve this problem, follow these steps:

1. Start IIS Manager. To do this, click Start, click Run, type inetmgr.exe, and then click OK.
2. In IIS Manager, expand server name, expand Web sites, and then click the website that you want to modify.
3. In the Features view, double-click Default Document.
4. In the Actions pane, click Enable.
5. In the File Name box, type the name of the default document, and then click OK.

Example here
//while using IIS enable Directory Browsing

steps:
1.Open CMD prompt run as admin mode

2.CD C:\Windows\Microsoft.NET\Framework64\v4.0.30319\
*press enter
3.aspnet_regiis -i
*press enter