What does the poet try to say?
Public Overrides Function GetBytes() As Byte() is obsolete: Rfc2898DeriveBytes replaces PasswordDeriveBytes for deriving key material from a password and is preferred in new applications.
Should i replace this one...
Dim keyBytes As Byte()
keyBytes = password.GetBytes(keySize / 8)
...with what?
You are missing crucial part of your code. It is that part that declares password to be PasswordDeriveBytes. Change that to Rfc2898DeriveBytes and you are good.