The File class is located in the System.IO namespace. Usually, you would have to call it by it's full name, eg:
Code:
If System.IO.File.Exists(CustomerFile) Then ...
But, to shorten things, you can use so called Imports. You can import namespaces, and you then no longer have to use the full names, but you can use 'abbreviations', like so:
Code:
'Top of code:
Imports System.IO
'...
'Somewhere in your code:
If File.Exists(CustomerFile) Then ...
If you did not import the namespace, VB will tell you it doesn't know the File class. You must have read over something explaining or at least telling you about importing the System.IO namespace.
The same is true (I think!) btw for the FileSystem class you tried the first time (although I'm not sure if it's also in System.IO or in some other namespace).