Login - Can't verify CSRF token authenticity

Hi, when I am logging in, sometimes I get this error. It would result in me unable to login at all. Any idea how does this error come from?

This result in the inability to even login to discourse.

I, [2016-03-17T17:05:20.078871 #4141]  INFO -- : Started POST "/session" for at 2016-03-17 17:05:20 +0800
I, [2016-03-17T17:05:20.134365 #4141]  INFO -- : Processing by SessionController#create as */*
I, [2016-03-17T17:05:20.136184 #4141]  INFO -- :   Parameters: {"login"=>"xx@gmail.com", "password"=>"[FILTERED]"}
W, [2016-03-17T17:05:20.137855 #4141]  WARN -- : Can't verify CSRF token authenticity
I, [2016-03-17T17:05:20.139322 #4141]  INFO -- :   Rendered text template (0.0ms)
I, [2016-03-17T17:05:20.140774 #4141]  INFO -- : Filter chain halted as :verify_authenticity_token rendered or redirected
I, [2016-03-17T17:05:20.142685 #4141]  INFO -- : Completed 403 Forbidden in 5ms (Views: 1.6ms | ActiveRecord: 0.0ms)

For the reference of the other folks who might have this problem:

I have initially set config.assets.prefix = ‘/’

Changing the asset directory to anything but / would solve this.