I followed these links:
You can add
<httpErrors errorMode="Custom" existingResponse="Replace">
<remove statusCode="404" subStatusCode="13" />
<error statusCode="404" subStatusCode="13" prefixLanguageFilePath="" path="http://localhost:1899/ErrorUpload.aspx" responseMode="Redirect" />
</httpErrors>
just after
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="5000000" />
</requestFiltering>
</security>
where you redirect to a Error Page...