title: String.Format() -- Input string was not in a correct format
body: <p>Getting this error on the <code>String.Format()</code> method and have no idea why, everything looks good to me?</p>
  
  <pre><code>string fontface = "";
  
  foreach(...)
  {
    fontface = String.Format(@"{3}
      @font-face {
          font-family: '{0}';
          src: url('{0}.eot');
          src: url('{0}.eot') format('embedded-opentype'),
                  url('{0}.woff2') format('woff2'),
                  url('{0}.woff') format('woff'),
                  url('{0}.ttf') format('truetype'),
                  url('{0}.svg#{0}') format('svg');
          font-weight:{1};
          font-style:{2};
      }"
    , family, weight, style, fontface);
  }
  </code></pre>