Note that in your code, you are actually instantiating two FileStream objects:
Code:
Dim f As FileStream = New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, 8192)
f = New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, 8192)
But, in the end, your f.Close() only closes the second one - you lose the reference to the first one when you reassign f on the second line of the code I copied.

The solution of your problem would be to delete one of the constructor calls so you only create one FileStream object. You can also condense the code to this:
Code:
Dim f As New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, 8192)