In your web.config, add this:
<system.webServer>
...
<handlers>
<add name="MiniProfiler" path="mini-profiler-resources/*" verb="*" type="System.Web.Routing.UrlRoutingModule" resourceType="Unspecified" preCondition="integratedMode" />
...
</handlers>
...
If you want some sweet MVC Action profiling (unrelated to your problem), add this line to Application_Start
in Global.asax.cs:
GlobalFilters.Filters.Add(new StackExchange.Profiling.MVCHelpers.ProfilingActionFilter());