WordPress Multisite on IIS throws 404 when saving changes

Hello guys,

I’ve installed WordPress Multisite on IIS server, everything is working fine, except when I’m trying to save the changes on a few pages (general, readings, … every page that is making a request to options.php) it throws “Not found”. Changes are saved, but I’m not redirected back. Here is my web.config.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
      <rewrite>
        <rules>
          <rule name="WordPress Rule 1" stopProcessing="true">
            <match url="^index\.php$" ignoreCase="false" />
            <action type="None" />
          </rule>
          <rule name="WordPress Rule 2" stopProcessing="true">
            <match url="^([_0-9a-zA-Z-]+/)?files/(.+)" ignoreCase="false" />
            <action type="Rewrite" url="wp-includes/ms-files.php?file={R:2}" appendQueryString="false" />
          </rule>
          <rule name="WordPress Rule 3" stopProcessing="true">
            <match url="^([_0-9a-zA-Z-]+/)?wp-admin$" ignoreCase="false" />
            <action type="Redirect" url="{R:1}wp-admin/" redirectType="Permanent" />
          </rule>
          <rule name="WordPress Rule 4" stopProcessing="true">
            <match url="^" ignoreCase="false" />
            <conditions logicalGrouping="MatchAny">
              <add input="{REQUEST_FILENAME}" matchType="IsFile" ignoreCase="false" />
              <add input="{REQUEST_FILENAME}" matchType="IsDirectory" ignoreCase="false" />
            </conditions>
            <action type="None" />
          </rule>
          <rule name="WordPress Rule 5" stopProcessing="true">
            <match url="(^[_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*)" ignoreCase="false" />
            <action type="Rewrite" url="{R:2}" />
          </rule>
          <rule name="WordPress Rule 6" stopProcessing="true">
            <match url="^([_0-9a-zA-Z-]+/)?(.*\.php)$" ignoreCase="false" />
            <action type="Rewrite" url="{R:2}" />
          </rule>
          <rule name="WordPress Rule 7" stopProcessing="true">
            <match url="." ignoreCase="false" />
            <action type="Rewrite" url="index.php" />
          </rule>
        </rules>
      </rewrite>
    </system.webServer>
</configuration>

Thanks in advance.