Hi Rocky,
Updating to Csla .NET 4.5.601 some .NET 4.0 projects under VS2010, I got plenty of errors and I could understand why. I migrated one of these projects to VS2012 and got the following error:
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(1605,5): warning MSB3268: The primary reference "Csla" could not be resolved because it has an indirect dependency on the framework assembly "System.Net.Http, Version=2.2.20.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which could not be resolved in the currently targeted framework. ".NETFramework,Version=v4.0,Profile=Client". To resolve this problem, either remove the reference "Csla" or retarget your application to a framework version which contains "System.Net.Http, Version=2.2.20.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a".
The important part is this one:
The primary reference "Csla" could not be resolved because it has an indirect dependency on the framework assembly "System.Net.Http, Version=2.2.20.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which could not be resolved in the currently targeted framework.
It turns out that a dependency is missing on the NuGet package,for .NET 4.0. Adding the NuGet package Microsoft.Net.Http to each project solved the iissue.