I have an ASP.NET form on which I have, among other controls, a web form button and an image contained within a DIV which is inititally set to be invisible. Javascript code is added to the web form button's OnClick event in the form's Page_Load event using the button's Attributes.Add() method to fire a client-side Javascript function which makes the image visible before firing the button's server-side code. The order of events when the web form button is clicked, then, should be:

1) Fire the javascript function to make the image visible
2) Fire the web form button's server-side code to complete processing

When the web form button is clicked, immediately after the image is made visible I get a client-side javascript error dialog box stating only a code line number and the message "Not implemented". If the button to not debug is clicked, the image remains visible, as expected, and the code proceeds to execute the server-side code as expected and the proper form postback is completed. If it is chosen to debug from the javascript error dialog, the line indicated is the HTML line defining the web form button containing the programmatically added OnClick event code.

I cannot see any problem with the code and have found no reference to this javascript error. Has anyone seen this before and what can be done about it?

Thanks,
Bill