Is it possible to update PHPMailer library to the most recent version found here on lgithub. It is the official source.
Currently you are using v. 5.1 most recent version is v5.2.1. The new version fixes a lot of bugs specially with TLS / SSL setups. Also some bugs with error reporting and languages have been fixed.
I've updated PHPMailer in my fork, I can create a pull request if you that is ok.