SSIS Script Failing in VS2015

I've hit what appears to be a show stopper in my quest to convince my organization to jump on the SQL2016 bandwagon.

It appears any SCRIPT task I attempt to run in VS2015 fails, with one trivial exception.

Here' the environment I am operating in:

SQL Server: Microsoft SQL Server 2016 (RTM-CU2) (KB3182270) - 13.0.2164.0 (X64)  Sep  9 2016 20:13:26   Copyright (c) Microsoft Corporation Developer Edition (64-bit) on Windows Server 2012 R2 Datacenter 6.3 <X64> (Build 9600: )

Visual Studio 2015: 14.0.23107.0 D14REL

Data Tools: 14.0.60923.0 (Released in June, 2016)

.NET Framework: 4.6.01055

After a bunch of monkeying around I opted to do the simplest test of all... A package that only has a single script task that does nothing.  Initially it runs successfully, but if I open it with the script editor, it fails.

The details of my test follows:

1. Create a SCRIPT TASK that only contains the default template for C#.
   1. OBSERVE: The SCRIPT task runs in VX2015 successfully.
2. Edit the SCRIPT task==>Edit Script==>Save it. (No code changes).
3. Exit the SCRIPT EDITOR.
4. In the SCRIPT EDITOR, hit OK.
   1. OBSERVE: Scripts contained in the package have compilation errors. Do you want to save the changes.
   2. Hit YES.
   3. OBSERVE: The SCRIPT TASK now has a RED X.
   4. The binary code for the script is not found. Please open the script in the designer by clicking Edit...

5. Back in the SCRIPT Editor attempt to BUILD the script:
   1. BUILD==>Build ST...
   2. OBSERVE:
      1. Unexpected exception: System.IO.FileNotFound Exception: could not load file or assembly 'System.Collections.Immutable, Version=1.1.37.0, Culture = neutral, ....

I know I'm not the first person to attempt to run a SCRIPT task in VS2015, but it sure feels like I'm deep in the woods.

What am I missing?

Thanks,