"Callback Error: Invalid response from server" from C# ASP.Net application

I have an ASP.Net application with a button containing the following Javascript to be invoked when it is clicked:-

    function calculate() {
        sectionIndex     = getSelectedRadioIndex("section");
        compositionIndex = getSelectedRadioIndex("composition");
        CallBackOU.callback( "calculate"   , sectionI开发者_开发知识库ndex, compositionIndex );
    }

I can verify that control reaches the last line of this function by setting a breakpoint on it. But instead of invoking the method in the code-behind file...

protected void CallBackOU_Callback (object sender, ComponentArt.Web.UI.CallBackEventArgs e)
{
    //blah blah
}

I get a dialogue reporting

Callback Error: Invalid response from server.

This dialogue appears three times, after which the page sits there doing nothing (forever, so far as I can make out).

I can't find any information about this. Can anyone give me any clues or pointers about how to go about diagnosing the problem?

Without seeing the signature of the calculate callback method this is only a shot in the dark but some issues i have encounter when invoking web methods from javascript are make sure the method is properly decorated [WebMethod], make sure the method is static, make sure the parameters are of the correct type and named properly (they are infact case sensitive when deserializing JSON iirc). A little more information regarding how the call is made (JSON/XML) and the signature might help. Also, you can try using fiddler to see if you get any more information regarding the error.