I installed CJBlog, and enabled it all. Then, when a member logged into Joomla from the front end, they were given 404 error.
I disabled all of CJBlog. Then, I enabled each part of CJ Blog, one item at a time, and tried to login from the front end. And cleared all Joomla cache between each attempt. It was the User - CJBlog plugin that caused the login problem.