title: cvs2svn fails with "xxx is not a valid ,v file"
body: <p>I finally found an answer to my question when I wanted to post it! However I'll still post it, including my answer, in case it helps someone else:</p>
  
  <p>When converting from CVS to Subversion cvs2svn failed on some files with the message</p>
  
  <pre><code>"xxx is not a valid ,v file"
  </code></pre>
  
  <p>What's the problem?</p>