title: Url encoded # (%23) causing 404 in ASP.NET application
body: <p>I have a deep-linking Silverlight RIA trying to consume a Twitter OAuth callback.  The URL of the callback &quot;page&quot; in the RIA is:</p>
  <pre><code>http://example.com/RiaTestPage.aspx#callback
  </code></pre>
  <p>Twitter calls back to this URL so long as the # sign is URL encoded; so the callback url I supply to Twitter is:</p>
  <pre><code>http://example.com/RiaTestPage.aspx%23callback
  </code></pre>
  <p>RiaTestPage.aspx does of course exist, but when Twitter calls back to this URL, I'm getting a 404 (from the VS 2010 ASP.NET Development server)</p>
  <blockquote>
  <p>Server Error in '/' Application</p>
  <p>The resource cannot be found.</p>
  <p>Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable.  Please review the following URL and make sure that it is spelled correctly.</p>
  <p>Requested URL: /RiaTestPage.aspx#callback</p>
  </blockquote>
  <p>Although the # sign has been correctly decoded in the error message above, the 404 seems to be the result of the encoded # sign.  If I manually change the callback url that caused the 404,</p>
  <pre><code>http://example.com/RiaTestPage.aspx%23callback
  </code></pre>
  <p>to this:</p>
  <pre><code>http://example.com/RiaTestPage.aspx#callback
  </code></pre>
  <p>The callback page in the RIA loads normally.  Why am I receiving a 404 in this situation?</p>