Website became restricted for logged on users after plugin update to 3.5.1.1

I have updated my plugin and faced with the problem. It displayed something about "failed to update role for visitor" or something like this when I updated it to version 3.5.1.1 and after that all users who trying to log on to the site see the page defined as "restricted".
Steps to reproduce: go to sign up form,enter your information and ubmit it. You will be unable to see the website just after that, all content will be blocked!
Help!