Hi. I am very new to StructureMap and am getting the following error:

StructureMap Exception Code: 202 No Default Instance defined for PluginFamily Company.ProjectCore.Core.IUserSession, Company.ProjectCore, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null

It seems to be hitting the first interface instance on compile and then throws the above error:

private readonly IUserSession _userSession;

public SiteMaster()
{
  _userSession = ObjectFactory.GetInstance<IUserSession>(); // ERROR THROWN HERE
  ...
}

For what it is worth, I have the PluginFamily reference above all of interfaces:

[PluginFamily("Default")]
public interface IUserSession

Below is my entire StructureMap.config

<StructureMap>
  <Assembly Name="Company.ProjectWeb" />
  <Assembly Name="Company.ProjectCore" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="MemCached" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.ICache"
      DefaultKey="MemCached" />
  <!--
  Use DefaultKey="Default" for sending the email
  in real time through the configured mail server 
  or use DefaultKey="MailQueue" to send the mail
  in batches through another process
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.IEmailService"
      DefaultKey="MailQueue" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="UserSession" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.IUserSession"
      DefaultKey="UserSession" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="Redirector" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.IRedirector"
      DefaultKey="Redirector" />
  <!--
  Use DefaultKey="Default" for standard cache 
  or DefaultKey="Navigation" for memcached cache.
  -->
  <PluginFamily
      Assembly="Company.ProjectCore"
      Type="Company.ProjectCore.Core.INavigation"
      DefaultKey="Navigation" />

Any suggestions? Thanks.