I had a problem with my members not being able to login after enabling DNS Blocklists and URI DNS Blocklists in the settings/security section of the admin panel.
I basically tried activating and deactivating all the various settings in the tools/ anti-spam tools section until I found the Culprit for my problem, also had to have a non admin user account for my site for testing.
DNS BLocklists - Second on the list of four,
"zomgbl.spameatingmonkey.net." - This is the one when deactivated that allowed my members to gain access again with all the rest remaining activated so on my site anyway this was a problem and it wasn't changed in any way from the original 7.0.9 clean install !
Thanks
Mike