Just because you created a StringCollection setting in the Settings list does not mean it holds a StringCollection object yet. You still need to create a New StringCollection:
Code:
My.Settings.yourSetting = New StringCollection()
This is exactly the same as when you are using a List(Of String) in normal code (which is a similar collection):
Code:
Dim list As List(Of String)
Now, list is Nothing and list.Count will not work. You first need to do:
Code:
Dim list As List(Of String)
list = New List(Of String)
As you may see, it's exactly the same thing: you need to create a new instance of an object before you can use it.