Scott,
I'm sorry you've run into issues. However, our SCLogin module calls Joomla's login code directly. For standard Joomla credentials, the SCLogin module does not actually perform any authentication, we've simply wrapped the normal Joomla login module with our own styles and a more configurable module. If other 3rd party extensions work, that doesn't mean too much as most, like EasySocial, perform the authentication process on their own.
Again, I'd recommend trying with the standard Joomla login module (mod_login) to see if you have the same issue. If so, that means that there is some underlying problem with the core Joomla login ability which should be investigated. If the mod_login module works, please put it and the SCLogin module on the same page so we can investigate the differences further to make sure you don't have this problem anymore.
Thanks,
Alex