Javascript function for custom validator control is not getting called

Hi folks,
This may be a stupid mistake of mine but javascript function for custom validator is not getting called. It is regular form with master page. I am using a Wizard control inside which I am validating user input for a particular step. If I do it on Server side then it works fine. Any idea? here is my code.
<asp:WizardStep runat="server" StepType="Step" Title="Comments"> <table style="width: 100%; height: 138px;"> <tr> <td style="width: 70px"> Comments<br />(only 20 charactrers )</td> <td style="width: 199px"> <asp:TextBox ID="txtbxComments" runat="server" Height="59px" TextMode="MultiLine"></asp:TextBox> </td> <td> ...