Error running node app in WebMatrix

I installed WebMatrix and followed these instructions to install IIS 7 on my Windows 7 machine.

When I click 'Run' to run my express node app, the browser pops up and tells me

The iisnode module is unable to start the node.exe process. Make sure the node.exe executable is available at the location specified in the system.webServer/iisnode/@nodeProcessCommandLine element of web.config. By default node.exe is expected to be installed in %ProgramFiles%\nodejs folder on x86 systems and %ProgramFiles(x86)%\nodejs folder on x64 systems.

Here is my web.config:

<configuration>
<system.webServer>

<handlers>
  <!-- indicates that the app.js file is a node.js application to be handled by the iisnode module -->
  <add name="iisnode" path="app.js" verb="*" modules="iisnode" />
</handlers>

<rewrite>
  <rules>
    <!-- Don't interfere with requests for logs -->
    <rule name="LogFile" patternSyntax="ECMAScript" stopProcessing="true">
      <match url="^[a-zA-Z0-9_\-]+\.js\.logs\/\d+\.txt$" />
    </rule>

    <!-- Don't interfere with requests for node-inspector debugging -->
    <rule name="NodeInspector" patternSyntax="ECMAScript" stopProcessing="true">
      <match url="^app.js\/debug[\/]?" />
    </rule>

    <!-- First we consider whether the incoming URL matches a physical file in the /public folder -->
    <rule name="StaticContent">
      <action type="Rewrite" url="public{REQUEST_URI}" />
    </rule>

    <!-- All other URLs are mapped to the Node.js application entry point -->
    <rule name="DynamicContent">
      <conditions>
        <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="True" />
      </conditions>
      <action type="Rewrite" url="app.js" />
    </rule>
  </rules>
</rewrite>

<!-- You can control how Node is hosted within IIS using the following options -->
<!--<iisnode      
      node_env="%node_env%"
      nodeProcessCountPerApplication="1"
      maxConcurrentRequestsPerProcess="1024"
      maxNamedPipeConnectionRetry="3"
      namedPipeConnectionRetryDelay="2000"      
      maxNamedPipeConnectionPoolSize="512"
      maxNamedPipePooledConnectionAge="30000"
      asyncCompletionThreadCount="0"
      initialRequestBufferSize="4096"
      maxRequestBufferSize="65536"
      watchedFiles="*.js"
      uncFileChangesPollingInterval="5000"      
      gracefulShutdownTimeout="60000"
      loggingEnabled="true"
      logDirectoryNameSuffix="logs"
      debuggingEnabled="true"
      debuggerPortRange="5058-6058"
      debuggerPathSegment="debug"
      maxLogFileSizeInKB="128"
      appendToExistingLog="false"
      logFileFlushInterval="5000"
      devErrorsEnabled="true"
      flushResponse="false"      
      enableXFF="false"
      promoteServerVars=""
     />-->

  <iisnode     
    nodeProcessCommandLine="&quot;%programfiles%\nodejs\node.exe&quot;"
    interceptor="&quot;%programfiles%\iisnode\interceptor.js&quot;" 
  />
</system.webServer>
</configuration>

What is causing this problem, and how do I fix it?

This is a common problem if you've installed the x64 version of node from the website. Currently IISNode is set up to read node.exe from the x32 path. You can either change nodeProcessCommandLine to use the full path to node.exe on your box, or install the 32 bit node install. We're working on fixing this so both 32/64 bit will work out of the box. Let me know if this turns out to not be the problem :)