Sounds like an old skin in a new blog. The way b2evolution provides file security changed, so old skins had a line that the new versions don't recognize thus you get that message.

You should briefly switch to the 'custom' skin that came with your distribution to verify this.

Thanks - how do I change skins when I can't see my blogs?

yourblog.com/admin.php should get you in the backoffice.
I was about to give the same answer as EdB this afternoon, but I realized this: the skin is for 1.10 and your blog is 1.10 so actually the skin should work.
You can download one of the similar skins form the same author (jibberjab) to see if the whole generation of skins fail, or that it' s just this single one.

Good luck

Thanks I have managed to find my admin area and change the skin and now its all working again.