One solution for HTTP Error 500.21 - Internal Server Error

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When I set IIS web server, I met multiple times about HTTP Error 500.21 – Internal Server Error.

I can not remember what the error screen exactly was, next time I must copy the screen.

I always forget how I got big help using a fast solution:

JUST RUN the command aspnet_regiis.exe –i

Very simple but you have to know it is not always working, but it is the one of you can choose to try.