Link in Activation email giving incorrect URL (please help urgent)

Hi,

I'm encountering a strange behavior with activation emails at my site http://www.mygrandsun.com

When users receive their activation email they get links containing 'blogrol'

like this:

http://ralf2.blogroll/wp-activate.php?key=

when it should be:

http://ralf2.mygrandsun.com/wp-activate.php?key=

Where may this me coming from?

(I've now disabled sign-up verification using the 'remove-email-verification' plug in but would like to fix the root of the problem, not just the symptom, as I'm sure this affects other areas as well.

Many thanks for your assistance.

Ralf