My multi-site installation at http://www.thinkbigsites.co.uk has a login redirect loop happening (this is something that's happened previously but was resolved and has suddenly re-occurred).
I have domain mapping installed on the multi-site and many sib-sites are using mapped domains. Interestingly, there's no issue logging in to mapped domains. However, if a user tries to log in to a sub-site that hasn't got a mapped domain (it's a sub-directory installation), there is a login redirect loop that won't allow them to log in to their website - which is not good!
I'm the only Super Admin and i have no problem logging in to any sub-site.
Your help would be very much appreciated.