title: MSBuild error when building <project> unrecognized
body: <p>I have installed VS2010.  I have a simple .build file which contains this.</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;project name="system" default="build"&gt;
      &lt;target name="build"&gt;
          &lt;exec program="C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\msbuild.exe"&gt;
              &lt;arg value="C:\System\system.build" /&gt;
          &lt;/exec&gt;
      &lt;/target&gt;
  &lt;/project&gt;
  </code></pre>
  
  <p>When I try to build the project by typing <code>C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe system.build</code>, I received this error. </p>
  
  <blockquote>
    <p>C:\System\system.build(2,1): error MSB4068: The element  is unrecognized, or not supported in this context.</p>
  </blockquote>
  
  <p>I'm interested in recommendations or suggestions. </p>