Multidomain + Domain Mapping + Buddypress error


I have a multi blog installation with multi-domain, domain-mapping and buddy press enabled.

One of the blog is hosted on sub-domain of one such additional domains and is mapped to its custom domain.

The issue is whenever the super admin, who is already logged in on the main wordpress blog, tries to login on this custom hosted domain blog, he gets the following error:

"Incorrect or out of date login key"

Please advise.