Sorry you ran into a problem. I'm not sure yet exactly why this happens, but I've taken some steps to hopefully fix it. I just made a change that I hope will fix this, but since I can't reproduce the problem on my own computer I'm not 100% sure. Can you try playing now and see if it's fixed?
If it still happens, please let me know via
http://warlight.net/ReportBug. Also, if it still happens, I have a temporary workaround. If you play via this special url, then I'm sure it won't happen:
http://warlight.net/MultiPlayer?AdPrm=1 . While AdPrm=1 is in your address bar, it shouldn't show the offending ad at all. This is just a temporary work-around so please be sure and also let me know if this helps you so I can make a permanent.
Thanks for reporting it!