خطا در migration

سلام

در جلسه 21 زمانی که میخواهیم tags ها را با استفاده از migration در پایگاه داده ذخیره کنیم به خطای زیر بر میخورم.

یعنی در واقع وقتی دستور Add-Migration add_tags را میزنم به خطا بر میخورم 

خوش حال میشم اگر راهنماییم کنید

Exception calling "LoadFrom" with "1" argument(s): "Could not load file or assembly 'file:///C:\Users\mahziar\documents\visual studio 
2015\Projects\mycms1\packages\EntityFramework.6.4.4\tools\EntityFramework.PowerShell.Utility.dll' or one of its dependencies. The system cannot find the file specified."
At C:\Users\mahziar\documents\visual studio 2015\Projects\mycms1\packages\EntityFramework.6.1.3\tools\EntityFramework.psm1:780 char:5
+     $utilityAssembly = [System.Reflection.Assembly]::LoadFrom((Join-P ...
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : FileNotFoundException
 
You cannot call a method on a null-valued expression.
At C:\Users\mahziar\documents\visual studio 2015\Projects\mycms1\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): "Could not load file or assembly 'file:///C:\Users\mahziar\documents\visual studio 
2015\Projects\mycms1\packages\EntityFramework.6.4.4\tools\EntityFramework.PowerShell.dll' or one of its dependencies. The system cannot find the file specified."
At C:\Users\mahziar\documents\visual studio 2015\Projects\mycms1\packages\EntityFramework.6.1.3\tools\EntityFramework.psm1:809 char:5
+     $domain.CreateInstanceFrom(
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : FileNotFoundException