An unknown error occurred while processing the request on the server. The status code returned from the server was: 500

Whenever you face the below error message

An unknown error occurred while processing the request on the server. The status code returned from the server was: 500

you can follow the steps and update you code files to come out from the error

open you .aspx page html view
add ValidateRequest = "false"  text in @Page directive.

Run the code, it should work fine :)

/AlpesH Shah