 <p>A couple ideas:</p> <ol> <li><p>Sometimes this can happen if there are oddities with your system clock or modified dates on the files. Try resetting the modified date. Maybe the easiest way is by zipping up the project, then extracting over top. Also of course delete your <code>.suo</code> and <code>.ncb</code> files.</p></li> <li><p>Make sure the <code>.h</code> file is IN the project tree. If it's <code>#include</code>d, but not specifically in the project tree, I don't believe VS will recognize changes always.</p></li> </ol>