How to Fix IIS HTTP 500.19 & 500.52 Errors in Reverse Proxy (ARR + URL Rewrite)

How to Fix IIS HTTP 500.19 & 500.52 Errors in Reverse Proxy (ARR + URL Rewrite)

If you are configuring IIS as a reverse proxy and see errors like:

• HTTP Error 500.19 – Internal Server Error

• HTTP Error 500.52 – URL Rewrite Module Error

• Error Code 0x8007000d

• Error Code 0x800700b7

• Outbound rewrite rules cannot be applied when the content is encoded ("gzip")

• Handler: ApplicationRequestRoutingHandler

This guide explains the exact cause and step-by-step solution.

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Understanding the Problem

When IIS is configured as a reverse proxy using:

• IIS URL Rewrite Module

• Application Request Routing

It forwards incoming traffic to a backend server (Node.js, .NET, etc.).

However, common configuration mistakes lead to two major errors:

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Error 1: HTTP 500.52 – Gzip + Outbound Rewrite Conflict

Error Message:

Outbound rewrite rules cannot be applied when the content of the HTTP response is encoded ("gzip")

Why This Happens

1. Browser sends:

   Accept-Encoding: gzip

2. IIS forwards this header to backend.

3. Backend responds with:

   Content-Encoding: gzip

4. IIS tries to apply outbound rewrite rules.

5. IIS cannot modify compressed (gzip) content.

6. Result: 500.52

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✅ Solution for 500.52

You must prevent the backend from sending compressed content.

Step 1: Allow Server Variable

IIS Manager → Server Level → URL Rewrite → View Server Variables Add:

HTTP_ACCEPT_ENCODING

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Step 2: Add This Rule in web.config (Inside <rules>)

<rule name="RemoveAcceptEncoding" stopProcessing="false">
    <match url=".*" />
    <serverVariables>
        <set name="HTTP_ACCEPT_ENCODING" value="" />
    </serverVariables>
    <action type="None" />
</rule>

This removes the gzip request header before proxying.

Restart IIS:

iisreset

✔ 500.52 resolved.

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Error 2: HTTP 500.19 – Invalid Configuration Data

This error usually shows:

Error Code: 0x8007000d

Meaning:

The configuration file contains invalid XML.

OR

Error Code: 0x800700b7

Meaning:

A configuration section is defined more than once.

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Common Causes of 500.19

1️⃣ Duplicate <rules> Section

❌ Invalid:

<rewrite>
    <rules>
    </rules>

    <rules>   <!-- second one -->
    </rules>
</rewrite>

✔ Only ONE <rules> block is allowed.

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2️⃣ Rule Outside <rules> Block

❌ Invalid:

<rewrite>
    <rules>
    </rules>

    <rule> <!-- illegal placement -->
</rewrite>

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3️⃣ URL Rewrite Module Not Installed

If your web.config contains:

<rewrite>

But the module is not installed, IIS throws 500.19.

Install:

• IIS URL Rewrite Module

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Correct Working Reverse Proxy web.config

Below is a properly structured, production-ready configuration:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.webServer>

    <rewrite>

      <rules>

        <!-- Remove Accept-Encoding to prevent gzip issue -->
        <rule name="RemoveAcceptEncoding" stopProcessing="false">
          <match url=".*" />
          <serverVariables>
            <set name="HTTP_ACCEPT_ENCODING" value="" />
          </serverVariables>
          <action type="None" />
        </rule>

        <!-- Reverse Proxy Inbound -->
        <rule name="ReverseProxyInboundRule1" stopProcessing="true">
          <match url="(.*)" />
          <action type="Rewrite" url="http://127.0.0.1:5000/{R:1}" />
        </rule>

      </rules>

      <outboundRules>
        <rule name="ReverseProxyOutboundRule1" preCondition="ResponseIsHtml">
          <match filterByTags="A, Form, Img"
                 pattern="^http(s)?://127.0.0.1:5000/(.*)" />
          <action type="Rewrite"
                  value="http{R:1}://api.yourdomain.com/{R:2}" />
        </rule>

        <preConditions>
          <preCondition name="ResponseIsHtml">
            <add input="{RESPONSE_CONTENT_TYPE}" pattern="^text/html" />
          </preCondition>
        </preConditions>
      </outboundRules>

    </rewrite>

  </system.webServer>
</configuration>

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Required IIS Configuration Checklist

✔ Install URL Rewrite ✔ Install ARR ✔ Enable Proxy in ARR ✔ Allow HTTP_ACCEPT_ENCODING variable ✔ Only one <rules> section ✔ Valid XML formatting

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How to Verify Everything

1. Browse directly:

   http://127.0.0.1:5000

   Must load successfully.

2. Restart IIS:

   iisreset

3. Test public domain.

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Final Summary

Error	Cause	Fix
500.52	Gzip + outbound rewrite conflict	Remove Accept-Encoding header
500.19 (0x8007000d)	Invalid XML	Fix web.config structure
500.19 (0x800700b7)	Duplicate section	Keep only one <rules> block

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If configured correctly, IIS reverse proxy with ARR and URL Rewrite will:

• Forward traffic to backend

• Rewrite outbound URLs

• Avoid gzip conflicts

• Run without 500 errors