The problem appears to be a timing issue caused by the speed of the server (among other things). I copied your source onto a local drive and loaded and reloaded with IE5. The problem did not occur unless I continually hit reload very fast. When I put it on my server with a heavy simulated load and network delay, the problem came up on reload. With a heavier delay it occurs even on the first load.
You have two main problems with the page, not actually the java script:
Your java script is intermixed with your HTML. Put all of your java script functions between the <HEAD> and </HEAD> tags. This will ensure that your functions are all loaded and precompiled in the virtual machine before your page tries to run them (ex: "onload=").
Also, you have a java script between your <FORM> and </FORM> tags. Since forms are loaded in the browser before being displayed, your script (a call to the UpdateModel() function) tries to get executed before your form elements (the "model" options) are fully loaded. To avoid this, put the script outside and below the <FORM> tag so the form elements are loaded before the the function call.
I made these two changes and could not get the error to recur.
Hope this helps.
-- Rich --
