I recently got this error when updating my rewrite rules in my system.webServer node of my web.config. The error message stated “HTTP Error 500.50 – URL Rewrite Module Error. The server variable “SERVER_PORT” is not allowed to be set. Add the server variable name to the allowed server variable list.”

Here is how you add a server variable using IIS

STEP 1 :

In your IIS with your website selected, select URL Rewrite option step1


Next select the View Server Variable option step2


Add server variable as shown below step3

Alternately you could also add through your web.config like below under <system.webServer></system.webServer> node.

<allowedServerVariables xdt:Transform="Insert">
    <add name="SERVER_PORT" />
    <add name="REMOTE_ADDR" />