EntityFramework DatabaseLogger Interceptor cannot be loaded on server

Adding DatabaseLogger Interceptor as per https://blog.oneunicorn.com/2014/02/09/ef-6-1-turning-on-logging-without-recompiling/

<interceptors>
  <interceptor type="System.Data.Entity.Infrastructure.Interception.DatabaseLogger, EntityFramework">
    <parameters>
      <parameter value="D:\TempLogging\LogOutput.txt"/>
      <parameter value="true" type="System.Boolean"/>
    </parameters>
  </interceptor>
</interceptors>

Works fine on local, dev and QA boxes but on customer server adding this config throws error

The type 'System.Data.Entity.Infrastructure.Interception.DatabaseLogger, EntityFramework' registered in the application config file as an IDbInterceptor could not be loaded

The EntityFramework.dll is in the server's bin directory.

Any ideas what could be causing the problem on this server? Any other things to check?