First off, before you start sending error reports, refresh the page. If the error continues, go to step two.
Step two, take a screenshot. This will make our lives simpler, or at least fixing the bug much simpler.
Step three, find your computer stats: What browser are you using? What operating system are you running (Vista, XP, Linux, etc)? What is your screen resolution? If you have more than one browser or computer with this error, include those stats too.
Step four, Upload the screenshot and post the link and stats to this forum.
That's all you do :) -Kat