yep, that is a bug
you could (temporarily just remove that javascript section.
it's trying (and failing) to decide which day is today and then css it accordingly to make it stand out on the calendar..
i don't have time to look deeper, but the fix is perty simple too, if you know some javascript
header.tpl loads up the value of the today variable as it stands in ubbthread "var today='17';" for example if you view this page's source.
so the solution would be (since you aren't getting that passed into the drupal) to populate today with the value of todays day in month. i can't remember off hand what it is in javascript, but it's googlable if you can't wait til i get back to it
edit: never mind.. add these two lines before that line of code
var ubbcal=new Date();
var today=ubbcal.getDay();
should do it
