Portal for ArcGIS authentication

Hi

We're using Essentials 4.2.1 and have recently upgraded to 10.3 Portal so are attempting to get Essentials to connect to it.  I can get Essentials Manager to authenticate against Portal ok, and from there it is possible to add private Portal content to a site.  The problem is that if I try to open a viewer from that site (HTML5 2.3 or Silverlight 2.3) then I get a message saying that access is denied, regardless of what security settings I use for the site.  Opening a site with non-private Portal content is fine however.  A bit more information:

• Our Portal is federated with ArcGIS Server, and Portal access is tied to Windows accounts so there is single sign-on.
• When I open Essentials Manager I first get a screen where I need to approve Essentials Manager to access my Portal account information.  No such screen comes up with the viewer but the viewer seems to try loading twice before the error message comes up.
• The following message is logged by Essentials:

<Event Timestamp="2015-05-22T11:58:04.7528904+12:00" Level="ERROR"><Message>[2015-05-22 11:58:04,749][ERROR][49  ][            ][Geocortex.GAS.Node.NodeEnvironment] Exception determining GasHome.

System.ArgumentNullException: Value cannot be null.

 

Parameter name: path1

 

   at System.IO.Path.Combine(String path1, String path2)

 

   at Geocortex.GAS.Node.NodeEnvironment.CreateLogDirectory()

 

   at Geocortex.GAS.Node.NodeEnvironment.CreateCompressedLogDirectory()

 

   at Geocortex.GAS.Node.NodeEnvironment..cctor()</Message></Event>

 

Any suggestions would be appreciated as at the moment we're not sure if the issue is with Essentials, the Portal upgrade or our infrastructure.

 

Thanks

Stuart