Frank,
You're missing the href on your anchor tag. While not all browsers require it since the onclick takes precedence, some do. Please add the following to your link, which basically has an href that intentionally does nothing:
href="javascript:void(0)"
That should fix you right up, but if not, please post a link to where you're implementing this so we can see. The other possible problem would be other Javascript errors on the page that are interfering with our login call.
Thanks,
Alex