The solution suggested
<system.webServer>
<modules runAllManagedModulesForAllRequests="true" >
<remove name="UrlRoutingModule"/>
</modules>
</system.webServer>
works, but can degrade performance and can even cause errors, because now all registered HTTP modules run on every request, not just managed requests (e.g. .aspx). This means modules will run on every .jpg .gif .css .html .pdf etc.
A more sensible solution is to include this in your web.config:
<system.webServer>
<modules>
<remove name="UrlRoutingModule-4.0" />
<add name="UrlRoutingModule-4.0" type="System.Web.Routing.UrlRoutingModule" preCondition="" />
</modules>
</system.webServer>
Credit for his goes to Colin Farr. Check-out his post about this topic at http://www.britishdeveloper.co.uk/2010/06/dont-use-modules-runallmanagedmodulesfo.html.