Hola deli.. estas segura de que tienes definida como public los métodos showfirst, next..etc..en tu codebehind..??
Cita: Public Sub ShowFirst(ByVal s As Object, ByVal e As EventArgs)
..
..
End Sub
Public Sub ShowPrevious(ByVal s As Object, ByVal e As EventArgs)
..
...
End Sub
Salu2