login submit button to image produces error

When attemting to change the login button on login.aspx to an image, the following error occurs:

There page at XXXXXX says:

There was a problem retrieving the XML data

Network error





It will not let me login. When changing back to a regular submit button (type='submit'), login works. I noticed these were hidden values as the page form loads. I would really like to use a custom button for this form.