Calender dates have moved

Hi, the dates posted in the calender have all moved a day!?
So something posted on a sunday has now popped up on the saturday, this is repeated every month.
Any ideas how this has happened and how to quick fix it?
I've not dome anything neither has anyone else, it just happend one day.
Cheers, stuart.
http://pdmc-motorcycle-club.forumotion.com/

Anyone?
Any suggestions that i can do to sort this? our calender is rather full with stuff and i i don't fancy moving every one of them a day.