The pasted below error only occurs when the solution has more than one project that references the EntityFramework.
When run the "Enable-Migrations" or "Add-Migration", I received the following error:

> 
> New-Object : The value supplied is not valid, or the property is
>  read-only. Change the value, and then try again. At
>  D:\Projetos\Monitoramento\packages\EntityFramework.6.1.3\tools\EntityFramework.psm1:757
>  char:13
>  + $info = New-Object System.AppDomainSetup -Property @{
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : InvalidData: (:) [New-Object], Exception
>  + FullyQualifiedErrorId : SetValueException,Microsoft.PowerShell.Commands.NewObjectCommand The
>  property 'PrivateBinPath' cannot be found on this object. Verify that
>  the property exists and can be set. At
>  D:\Projetos\Monitoramento\packages\EntityFramework.6.1.3\tools\EntityFramework.psm1:772
>  char:9
>  + $info.PrivateBinPath += ';lib\net45'
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : InvalidOperation: (:) [], RuntimeException
>  + FullyQualifiedErrorId : PropertyNotFound Exception calling "LoadFrom" with "1" argument(s): "The specified path, file name, or
>  both are too long. The fully qualified file name must be less than 260
>  characters, and the directory name must be less than 248 characters."
>  At
>  D:\Projetos\Monitoramento\packages\EntityFramework.6.1.3\tools\EntityFramework.psm1:780
>  char:5
>  + $utilityAssembly = [System.Reflection.Assembly]::LoadFrom((Join-Path $ToolsP ...
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : NotSpecified: (:) [], MethodInvocationException
>  + FullyQualifiedErrorId : PathTooLongException You cannot call a method on a null-valued expression. At
>  D:\Projetos\Monitoramento\packages\EntityFramework.6.1.3\tools\EntityFramework.psm1:781
>  char:5
>  + $dispatcher = $utilityAssembly.CreateInstance(
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : InvalidOperation: (:) [], RuntimeException
>  + FullyQualifiedErrorId : InvokeMethodOnNull Exception calling "CreateInstanceFrom" with "8" argument(s): "The specified path, file
>  name, or both are too long. The fully qualified file name must be less
>  than 260 characters, and the directory name must be less than 248
>  characters." At
>  D:\Projetos\Monitoramento\packages\EntityFramework.6.1.3\tools\EntityFramework.psm1:809
>  char:5
>  + $domain.CreateInstanceFrom(
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : NotSpecified: (:) [], MethodInvocationException
>  + FullyQualifiedErrorId : PathTooLongException
> 
> 
> 

Output with EntityFramework 6.1.1:

> 
> Exception calling "LoadFrom" with "1" argument(s): "The specified
>  path, file name, or both are too long. The fully qualified file name
>  must be less than 260 characters, and the directory name must be less
>  than 248 characters." At C:\Users\Hudson\Documents\Visual Studio
>  2015\Projects\WpfApplication4\packages\EntityFramework.6.1.1\tools\EntityFramework.psm1:780
>  char:5
>  + $utilityAssembly = [System.Reflection.Assembly]::LoadFrom((Join-Path $ToolsP ...
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : NotSpecified: (:) [], MethodInvocationException
>  + FullyQualifiedErrorId : PathTooLongException You cannot call a method on a null-valued expression. At
>  C:\Users\Hudson\Documents\Visual Studio
>  2015\Projects\WpfApplication4\packages\EntityFramework.6.1.1\tools\EntityFramework.psm1:781
>  char:5
>  + $dispatcher = $utilityAssembly.CreateInstance(
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : InvalidOperation: (:) [], RuntimeException
>  + FullyQualifiedErrorId : InvokeMethodOnNull Exception calling "CreateInstanceFrom" with "8" argument(s): "The specified path, file
>  name, or both are too long. The fully qualified file name must be less
>  than 260 characters, and the directory name must be less than 248
>  characters." At C:\Users\Hudson\Documents\Visual Studio
>  2015\Projects\WpfApplication4\packages\EntityFramework.6.1.1\tools\EntityFramework.psm1:809
>  char:5
>  + $domain.CreateInstanceFrom(
>  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  + CategoryInfo : NotSpecified: (:) [], MethodInvocationException
>  + FullyQualifiedErrorId : PathTooLongException
> 
> 
>