My own validator doesn't validate on serverside

Hey, 
 Ik have created my own validator and everything works fine on the client side, but when I disable javascript, the serverside validation fails to let the page know there was an error. The EvaluateIsValid method is fired, but even when it returns false, the code behind of the page is still executed. Can someone help me ? This is my code :
 
1 namespace Validators
2 {
3 [DefaultProperty("Text")]
4 [ToolboxData("&lt;{0}:RequiredNumberValidator runat=server></{0}:RequiredNumberValidator>")]
5 public class RequiredNumberValidator : BaseValidator
6 {
7 [Bindable(true)]
8 [Category(" ...