Omer, I am using Firefox.
Now with enabled DEBUG mode I see following error:
Most likely you have turned on "Verify Email" feature in admin panel.
So user registers, then system tries to send verification email, but can't send it because of issues with php mail() function on your server.
What to do.
You will need to contact your host and ask whether php mail() function is enabled on your server.
If they will not be able to help you, then you will need to enable SMTP and set up CRON.
But contact your host first. Most likely they will be able to solve this issue for you.
More info:
http://www.oxwall.org/forum/topic/14430