Q:

Sudden Certificate Verify Failed on Xero Public Application

Our staging server is connecting to our Xero Public Application perfectly fine, that is up until now (Dec 7, 2016). For some strange reason it is now returning the following error:
OpenSSL::SSL::SSLError: SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed
Here is the code snippet that we are using to connect to Xero. 

@xero_client = Xeroizer::PublicApplication.new(APP_KEY, APP_SECRET,
   :logger => Logger.new('log/xero.log', 'weekly')
request_token = @xero_client.request_token(:oauth_callback 
    => "#{APP_DOMAIN}/oauth/callback")

Then the app fails at this line, and throws the SSLError specified above. 
Anyone knows the root cause of this?
Details:

We are using Ubuntu 14.04 (Trusty)
We are using Ruby on Rails 4.1.7, Ruby 2.1.8p440
We are using Xeroizer 2.16.4 gem
SSL on the server seems OK, as per checking with 3rd-party sites that check if SSL is properly installed in the site;
Changing the APP_KEY and APP_SECRET to a Partner Application and changing the constructor to Xeroizer::PartnerApplication, and adding relevant extra parameters works (meaning server SSL installation is not the issue). 

A:

We were running in to this problem as well - updating to version 2.16.5 of the Xeroizer gem resolved the issue for us.

