Changed teh build output to diagnostic and found this. Ran the upgrade wizard on the SL project to double check and got the same result.
warning : Client proxy generation for service 'NU.SubStationAccess.Web.Services.SubStationAccess' failed: Microsoft (R) Silverlight Service Model Proxy Generation Tool
warning : [Microsoft (R) Silverlight SDK, Version 4.0.50826.0]
warning : Copyright (c) Microsoft Corporation. All rights reserved.
warning : Error: Cannot load reference assembly
'C:\Program Files (x86)\Telerik\RadControls for Silverlight Q2 2010 SP1\Binaries\Silverlight\Telerik.Windows.Controls.Data.dll'
warning : Cannot load file C:\Program Files (x86)\Telerik\RadControls for Silverlight Q2 2010 SP1\Binaries\Silverlight\Telerik.Windows.Controls.Data.dll as an Assembly. Check the FusionLogs for more Information.
warning : Could not load file or assembly 'file:///C:\Program Files (x86)\Telerik\RadControls for Silverlight Q2 2010 SP1\Binaries\Silverlight\Telerik.Windows.Controls.Data.dll' or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)
warning : An attempt was made to load an assembly from a network location which would have caused the assembly to be sandboxed i
n previous versions of the .NET Framework. This release of the .NET Framew...