I used prevoius version of elmah in my asp.net mvc application and there I had to modify web config. For example I had to add this lines :
<system.webServer>
.....
<handlers>
<remove name="MvcHttpHandler" />
<remove name="UrlRoutingHandler" />
<add name="Elmah" verb="POST,GET,HEAD" path="elmah.axd" preCondition="integratedMode" type="Elmah.ErrorLogPageFactory, Elmah" />
<add name="MvcHttpHandler" preCondition="integratedMode" verb="*" path="*.mvc" type="System.Web.Mvc.MvcHttpHandler, System.Web.Mvc, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />
</handlers>
</system.webServer>
<system.web>
....
<httpHandlers>
<add verb="POST,GET,HEAD" path="elmah.axd" type="Elmah.ErrorLogPageFactory, Elmah" />
<add verb="*" path="*.mvc" validate="false" type="System.Web.Mvc.MvcHttpHandler, System.Web.Mvc, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />
</httpHandlers>
</system.web>
But now, with nuget installation, is it necessary to manually modify web.config ?