serverclick event is not fired when onclick javascript returns true?

I have a html input button like this

<input type="button" id="send_button" class="form_button" value="Send" onclick="return validateTextBoxes();" runat="server" />

And also I have javascript

<script language="javascript">        
    function validateTextBoxes() 
    {            

            var reading1 = document.getElementById('<%= meterReading1.ClientID%>').value;           
            var error = document.getElementById('<%= lblError.ClientID%>');  
            var btn = document.getElementById('<%= send_button.ClientID%>');  
            var ValidationExpression = /[\d]/;     
            if (reading1 == "" )    
            {
    开发者_如何学JAVA            error.innerHTML = "Please enter Water Meter Reading.";  
                return false;
            }
            else if(!ValidationExpression.test(reading1))           {
                error.innerHTML = "Please enter valid Meter Reading(It Contains only numbers)"; 
                return false;
            }
            else
            {
                error.innerHTML = "";
                return true;
            }

    }    
 </script>

And I am also calling this server click event in the code behind file this.send_button.ServerClick += new System.EventHandler(this.send_ok);

So here is the problem when javscript returns true its not firing the serverclick event.

Please help me where I am doing wrong(I am using framework 1.1)

Thanks

I had this problem once and I actually had to do something like this:

onclick="if (validateTextBoxes()) { return true; } else { return false; }"

You absolutely should not have to do this and it made no sense to me why it would be have this way, but alas, I tried it and it worked :(