error: BC30451:Name 'IsNumeric' is not declared???

Hi there,

im having a problem compliling a custom control to a dll using dos

here is the code

Imports System.ComponentModel
Imports System.Web.UI
Imports System.Web

Namespace TestYear
<DefaultProperty("Text"), ToolboxData("<{0}:PubYear runat=server></{0}:PubYear>")> Public Class PubYear
Inherits System.Web.UI.WebControls.TextBox
Implements INamingContainer

Private _text As String = "" 
Private _response As String

Public Sub New()
Text = " "
End Sub

Public Overrides Property Text() As String
Get
Return _text
End Get
Set(ByVal Value As String)
_text = Value
End Set
End Property

Public Property Response() As String
Get
Return _response
End Get
Set(ByVal Value As String)
_response = Value
End Set
End Property

Private Sub PubYear_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.TextChanged
If Text = "" Then
Response = "Enter the Contact Number"
Else
If Not IsNumeric(Text) Then
Response = "Enter a valid Contact Number"
Else
Response = "" 
End If
End If
End Sub

End Class
End Namespace



When i go to compile i get the folowing error message:

error: BC30451:Name 'IsNumeric' is not declared

Can any one understand why, i wouldnt think it would need to be as i was under the impression it is a built in function???

any help would be appreciated!  Thanks!