Below are the contents of the config file. I added the top three nodes and adjusted the url for my server based on an answer that helped someone solve their problem with the same error message. It didn't solve mine. I've no idea what else needs to be here or what a working config file should look like.

<Configuration>

<ReportServerUrl>http://sql01/ReportServer</ReportServerUrl&gt;

<ReportServerVirtualDirectory></ReportServerVirtualDirectory>

<ReportBuilderTrustLevel>FullTrust</ReportBuilderTrustLevel>

<Extensions>

<DeliveryUI>

<Extension Name="Report Server Email" Type="Microsoft.ReportingServices.EmailDeliveryProvider.EmailDeliveryProviderControl,ReportingServicesEmailDeliveryProvider">

<DefaultDeliveryExtension>True</DefaultDeliveryExtension>

<Configuration>

<RSEmailDPConfiguration>

<DefaultRenderingExtension>MHTML</DefaultRenderingExtension>

</RSEmailDPConfiguration>

</Configuration>

</Extension>

<Extension Name="Report Server FileShare" Type="Microsoft.ReportingServices.FileShareDeliveryProvider.FileShareUIControl,ReportingServicesFileShareDeliveryProvider"/>

</DeliveryUI>

</Extensions>

<Add Key="MaxActiveReqForOneUser" Value="20"/>

<Add Key="DisplayErrorLink" Value="true"/>

</Configuration>