error of install EntityFramework in Visual Studio 2013 win 7

I am working on RESTful Web services design in Visual Studio 2013 win 7.

I need to run the command of "Enable-Migrations" to ennables Code First Migrations in a project.

This can add a Migrations folder to my project. And there will be a Configuration.cs in the folder.

I need to install a new version of EntityFramework.

When I installed it , I got error:

 PM> Install-Package EntityFramework -IncludePrerelease
 Installing 'EntityFramework 6.1.3-beta1'.
 You are downloading EntityFramework from Microsoft, the license    agreement to which is available at http://go.microsoft.com/fwlink/?LinkID=xxxxxxx. 

 Successfully installed 'EntityFramework 6.1.3-beta1'.
 Do you want to run software from this untrusted publisher?

 File \\Mypath\packages\EntityFramework.6.1.3-beta1\tools\init.ps1 is    published by CN=Microsoft Corporation, OU=MOPR, O=Microsoft Corporation, L=Redmond, S=Washington, C=US and is not trusted on your system. Only run scripts from trusted publishers.

[V] Never run  [D] Do not run  [R] Run once  [A] Always run  [?] Help (default is "D"):R

Do you want to run software from this untrusted publisher?

File \\Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.psm1 is published by CN=Microsoft Corporation, OU=MOPR, O=Microsoft Corporation, L=Redmond, S=Washington, C=US and is not trusted on your system. Only run scripts from trusted publishers.

[V] Never run  [D] Do not run  [R] Run once  [A] Always run  [?] Help (default is "D"):R

Adding 'EntityFramework 6.1.3-beta1' to ProductReviews.
Successfully added 'EntityFramework 6.1.3-beta1' to ProductReviews.

Do you want to run software from this untrusted publisher?

File \\Mypath\packages\EntityFramework.6.1.3-beta1\tools\install.ps1 is published by CN=Microsoft Corporation, OU=MOPR, O=Microsoft Corporation, L=Redmond, S=Washington, C=US and is not trusted on your system. Only run scripts from trusted publishers.

[V] Never run  [D] Do not run  [R] Run once  [A] Always run  [?] Help  (default is "D"):R

 Exception calling "LoadFrom" with "1" argument(s): "Could not load file or assembly 'file://\\Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.PowerShell.Utility.dll' or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)"

 At \\Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.psm1:780 char:62
  +     $utilityAssembly = [System.Reflection.Assembly]::LoadFrom <<<< ((Join-Path $ToolsPath EntityFramework.PowerShell.Utility.dll))
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException

You cannot call a method on a null-valued expression.
At \\Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.psm1:781 char:50
 +     $dispatcher = $utilityAssembly.CreateInstance <<<< (
 + CategoryInfo          : InvalidOperation: (CreateInstance:String) [], RuntimeException
 + FullyQualifiedErrorId : InvokeMethodOnNull

 Exception calling "CreateInstanceFrom" with "8" argument(s): "Could not load file or assembly 'file:// \\Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.PowerShell.dll' or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)"

 At \\Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.psm1:809 char:31
 +     $domain.CreateInstanceFrom <<<< (
 + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException

 Exception calling "LoadFrom" with "1" argument(s): "Could not load file or assembly 'file://\\Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.PowerShell.Utility.dll' or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)"

  At \\ Mypath\packages\EntityFramework.6.1.3-beta1\tools\EntityFramework.psm1:780 char:62
  +     $utilityAssembly = [System.Reflection.Assembly]::LoadFrom <<<< ((Join-Path $ToolsPath EntityFramework.PowerShell.Utility.dll))
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : DotNetMethodException

I do not understamd the error. How to solve it ? Thanks !

UPDATE

I can build the project by using local drive now.

But, I got a new error, please see the attached pic.

Your error means to be related to your used network share (\Mypath).

Microsoft applied a security update to harden UNC path with last patchday. Maybe this causes our issue. I never used network share to create projects. I always use local paths and commit changes into a version control software. The second issue is a new question. Provide more details about your model and the error in a new question.