Thanks for your reply David. But I have already created an unsubscribe page and have the URL of thi spage in the settings for the site correctly. My problem is the token {% UnsubscribeLink %} does not get replaced and it renders empty.
I also tried to build the link myself as in <a href="http://mysite.com/unsubscribe.aspx?subscriberguid={%SubscriberGUID%}&newsletterguid={%NewsletterGUID%}&issueid={%IssueID%}">Click here to unsubscribe</a>
but this doesn't work either because non of the tokens ({%SubscriberGUID%}, {%NewsletterGUID%}, {%IssueID%}) are getting replaced when the newsletter is sent.
It is as if it is not possible to have an unsubscribe link with 'dynamic newsletters'! And I naturally question this as there is a field in the configuration section of dynamic newsletter called "Unsubscription page URL:" which makes me think either there is something I am doing wrong or this is a bug.