The name you are using for the property is not valid as identifier names should not start with underscore. Usually the compiler will throw an error about this, however in this case it doesn't.
You should use getCounter() As String
in this case Counter is considered by the compiler as a property !
So you should return a value for Counter.
You could also use setCounter to set the Counter property.
If you want the routin being a subroutine you could use GetCounter or Get_Counter, in this case they will be considered as routines and not as Properties.