Updating Users Attributes with a .csv file and Set ADUser where every attribute entry is unique.

Hope someone will help. Newbie to this Forum, apologies if I offend. I have exported an list of user sAMAccountnames from AD domain and forest level 2008 r2. 

I have extended the schema to add a new attribute called barcode. 

I need to take a .csv with each user and their new barcode number and add it to the attribute "barcode".

I'm using a .csv file with a test users in it to get the Script right, the file is named adtest.csv

I'm using the Administrator:Active Directory module for Windows Powershell 

I'm using a sample script as a basis from here:"http://itknowledgeexchange.techtarget.com/powershell/bulk-modifications-using-set-aduser/"

# Import CSV into variable $userscsv$users=Import-Csv-PathC:\Scripts\adtest.csv# Loop through CSV and update users if the exist in CVS fileforeach($userin$users){#Search in specified OU and Update existing attributesGet-ADUser-Filter"SamAccountName -eq '$($user.samaccountname)'"-Properties*-SearchBase"cn=Students,cn=Users,DC=OURDOMAIN,DC=LOCAL"|Set-ADUser-Replace@{l="$($user.barcode)"}}

I'm getting this Error:

Get-ADUser : Directory object not found
At line:3 char:2
+  Get-ADUser -Filter "SamAccountName -eq '$($user.samaccountname)'"
-Properties * ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~
    + CategoryInfo          : ObjectNotFound: (:) [Get-ADUser], ADIdentityNotF
   oundException
    + FullyQualifiedErrorId : ActiveDirectoryCmdlet:Microsoft.ActiveDirectory.
   Management.ADIdentityNotFoundException,Microsoft.ActiveDirectory.Managemen
  t.Commands.GetADUser