Okay @Mathkar_kunal
You are iterating through each string and you are getting error like: User does not exist.
Just create a empty list above your loop
myList = New List(Of String())
and put a try catch in for each activity in try block put all your activities, and in catch block use Append Item to Collection Activity.
At the end you will get all the Users which will throw an error!
Best regards,
Ajay Mishra