ASP:TextBox or ASP:CheckBoxList, throwing Javascript errors when Requiredfield validator is there

I have created a User Control for my SharePoint, which has a simple TextBox and a CheckBoxList. For both of these controls, I have ASP:RequiredFieldValidator and ASP:RegularExpressionValidator.

When I select some item in the CheckBoxList or type some input in the TextBox, I am getting a javascript error in some unknown location. (This is not accepted by my customer.)

Now, when I debug this using FireBug, in the console I see validators[i] is null. It is actually failing in the JS code generated by these validators.

Can some one help me?

Edited:

<asp:TextBox ID="txtNumbers" runat="server" CssClass="Label4" ></asp:TextBox>
                                    <asp:RegularExpressionValidator ID="RegularExpressionValidatorGPC" runat="server"
                                        ControlToValidate="txtNumbers" ErrorMessage="Only Numbers Accepted "
                                        ValidationExpression="^\d+$"
                                        SetFocusOnError="true"></asp:RegularExpressionValidator>
                                    <asp开发者_运维知识库:RequiredFieldValidator ID="RequiredNUMValue" runat="server" ControlToValidate="txtNumbers"
                                        SetFocusOnError="true" ErrorMessage="Please enter a valid number"></asp:RequiredFieldValidator>

Also, I added required field validators for RadioButtonList (not CheckBoxList).

<asp:RadioButtonList ID="rbtOptions" runat="server" CssClass="Label3">
                                        <asp:ListItem Text="Option 1" />
                                        <asp:ListItem Text="Option 2" />
                                    </asp:RadioButtonList>
                                    <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="rbtOptions"
                                        SetFocusOnError="true" ErrorMessage="Please Select a Valid Option"></asp:RequiredFieldValidator>

When I either input any text in the TextBox or select any option, there is a JavaScript error.

There is something else on your page that is conflicting with this. Taking what you posted and trying a simple page it works as it should, so I'm assuming that there's other elements / scripts that are causing this.

<div>
    <asp:TextBox ID="txtNumbers" runat="server" CssClass="Label4"></asp:TextBox>
    <asp:RegularExpressionValidator ID="RegularExpressionValidatorGPC" runat="server" ControlToValidate="txtNumbers" ErrorMessage="Only Numbers Accepted " ValidationExpression="^\d+$" SetFocusOnError="true"></asp:RegularExpressionValidator>
    <asp:RequiredFieldValidator ID="RequiredNUMValue" runat="server" ControlToValidate="txtNumbers" SetFocusOnError="true" ErrorMessage="Please enter a valid number"></asp:RequiredFieldValidator>
    <asp:RadioButtonList ID="rbtOptions" runat="server" CssClass="Label3">
        <asp:ListItem Text="Option 1" />
        <asp:ListItem Text="Option 2" />
    </asp:RadioButtonList>
    <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="rbtOptions" SetFocusOnError="true" ErrorMessage="Please Select a Valid Option"></asp:RequiredFieldValidator>
    <asp:Button ID="btnSubmit" runat="server" Text="submit" />
</div>

Do you have any script tags, or other elements in your markup that could be interfering with this?

Self closed tags can cause issues like this ( is a no no)