Build Fails: Help to discern Error message, please

Background: Created Project in Unity 4.6 as web, then Android.
copied the project and imported it (took forever) into Unity 5. Seems happy. Plays nicely in the editor.
Changed the Build to Windows Store: Universal 8.1
Set all the settings within Player settings.
(Using Net Core) for Compilation Overrides.

Set: Build and Run on : Local Machine
Set: Debugging: Unity C# Projects

(Not using: Development build)

When I “Build” I’m saving this to a local folder on the computer)

And I get this, after a few seconds:
Assets\DataReceiver.cs(60,24): error CS1061: ‘System.IO.MemoryStream’ does not contain a definition for ‘GetBuffer’ and no extension method ‘GetBuffer’ accepting a first argument of type ‘System.IO.MemoryStream’ could be found (are you missing a using directive or an assembly reference?)

Looking at DataReceiver.cs, I believe this is a Unity script, and I know it’s not mine.

More errors follow:

Assets\DataReceiver.cs(61,3): error CS1502: The best overloaded method match for ‘System.Array.Copy(System.Array, int, System.Array, int, int)’ has some invalid arguments

Assets\DataReceiver.cs(61,22): error CS1503: Argument 2: cannot convert from ‘long’ to ‘int’

Assets\Utils.cs(12,10): error CS1501: No overload for method ‘GetString’ takes 1 arguments

Error building Player because scripts had compiler errors

System: Windows 8.1 64 bit (with unity personal 64 bit)
.net versions 4.5 & 4.5.1 installed.

Tried: Changing the Compilation Overrides within Player settings, from Use Net Core to: Use Net Core Partially
but get this extra Error along with the ones above:

Assets\DataReceiver.cs(61,3): error CS1502: The best overloaded method match for ‘System.Array.Copy(System.Array, int, System.Array, int, int)’ has some invalid arguments

Assets\Scripts\MoveObjectLeftOntoScreen.cs(8,29): error CS0570: ‘Hash’ is not supported by the language

Note: I save my project settings each time I change the Player Settings mentioned above.

I have also tried building to an alternate location, but no go.

Any thoughts? Oh, Unity Version is: 5.0.0.0f4

Hmmm…

Tried my last resort: Went to Player Settings: Compilation Overrides: and set it to: None

And the build was successful… On to the next step of porting!

You’ll still have to fix those errors, setting Compilation Overrides to None only chooses different compiler for those scripts. When you’ll try to pass Windows App Certification, they’ll reappear.