 <p>First, of course, your application must declare that it is doing serial communication in the application manifest: </p> <pre><code>&lt;DeviceCapability Name="serialcommunication"&gt; &lt;Device Id="vidpid:xxxx xxxx"&gt; &lt;Function Type="name:serialPort"/&gt; &lt;/Device&gt; &lt;/DeviceCapability&gt; </code></pre> <p>Could this be the missing bit?</p>