Under IIS7 there’s a new setting that prevents large content being sent to the server. If your using NeatUpload then you will see the error as a 404. However you might want to allow for such large content for example posting a video file to the server. The trick is to update the maxAllowedContentLength attribute which can be easily done from your web.config file like so.

<system.webServer> 
    <security> 
      <requestFiltering> 
        <requestLimits maxAllowedContentLength="314572800"> 
          <headerLimits> 
          </headerLimits> 
        </requestLimits> 
      </requestFiltering> 
    </security> 
</system.webServer>