title: Java compiler level does not match the version of the installed Java project facet
body: <p>I have created a New Dynamic Project under Eclipse Helios Version, where my JRE Version is set to 1.6.
  I have added Maven capabilities to the Web Application by clicking on <em>Configure</em> → <em>Convert to Maven Project</em>.</p>
  
  <p>After adding this, a build error appeared in the Eclipse Problems view:</p>
  
  <pre><code>Java compiler level does not match the version of the installed Java project facet.
  Unknown Faceted Project Problem (Java Version Mismatch)
  </code></pre>
  
  <p>Please tell me how to resolve this error (I want to have my JRE version as 1.6 only).</p>