Server Error on WooCommerce check out

We have been using this Plug in for about two months with no issues, works perfectly with our paid Google business Gmail account using Oauth 2.0. On the 30th of December however my customers upon completing check out were no long being directed to the order conformation page and the sale conformation email being sent out, instead a server error message was going up and no email was going out to the customer, only the site admin. the sale was being recorded and credit card processed but the customer was being led to believe the sale didn’t go through. We have a private VPS, no changes have been made on the server or the site. We had to shut down the SMTP plugin because of the nature of how it is messing up our store check out. The only thing we know is that this behavior started on or about December 30th.