Weird thing going on

Hi. I have the classified theme.
New user registers and it says on the end registration failed, but in reality when clicking the back arrow user is signed in as the dashboard, favorite, logout buttons are displayed and working.

Now when the
User logs out, then when logs back in, it says “you don’t have sufficient permission to access this page”, clicking the back arrow and refreshing the page the user is logged in. Other times it says; blocked
but it also logs the user in when back arrow and refresh.
I am using the latest wordpress as of 14-06-2015

Any idea what is going on?? Irritating, because most people are novices and wont even think of working it out and just leaves. I would really appreciate if someone can advise me on this fix. No coding changed the theme is the way it came accept some minor basic css change.
Thanx a lot.