BuddyPress and https

I've been setting up a buddypress site with 4 underlying blogs and was originally using the default buddypress theme with some tweaking.

I decided to try out some of the buddypress themes available (using corporate right now) The WPMU DEV themes call on https pages which do not exist in my intsallation . . . why is that?

That is - my site works fine with the buddypress default them - but with a WPMU DEV theme it does not work as when "members", for example is clicked - it goes to an https page giving a "not found error".

Why would the theme do this?

Thanks